POOL A - ULSTER v MUNSTER (at Ravenhill, Belfast, 7.35pm).
Munster, the only unbeaten side in Pool A travel to Belfast hoping to repeat last season's 15 - 9 Celtic League semi-final victory over the 1999 Heineken Cup champions.
Both sides are missing their Irish international players who are preparing for Saturday's World Cup qualifier against Georgia in Dublin.
Ulster will be captained by Irish international lock Jeremy Davidson in the absence of the injured Andy Ward, and after a fine performance against Neath last weekend, Adam Larkin continues at fly half.
Mick Galway skippers Munster due to an injury to Jim Williams. Williams has a damaged knee, and coach Alan Gaffney is wary of risking the influential flanker.
"Jim's injury is not too serious, a little swelling on the knee, but at this stage of the season we're not prepared to take chances," said Gaffney.
"It is never easy to get anything out of Ravenhill and we can expect a capacity crowd to get right behind Ulster. It's a game they know they must win. So all in all, I'd say we're right up against it."
Ulster: B Cunningham; J Topping, R Constable, J Bell, T Howe; A Larklin, N Doak; J Fitzpatrick, M Sexton, R Kempson, M Blair, J Davidson (capt), W Brosnihan, T McWhirter, N McMillan. Replacements: S Best, P Shields, P Johns, N Best, K Campbell, S Stewart, S Young.
Munster: J Staunton; D Crotty, M Mullins, J Holland, M Lawlor; K Keane, M Prendergast; M Horan, F Sheahan, R Laffan, M Galwey (capt), M O'Driscoll, D O'Callaghan, E Halvey, D Leamy. Replacements: J Blaney/J Fogarty, S Kerr, T Hogan, C McMahon, D Malone, C Mahony, C Huppert.
Referee: P Adams (Wales).
Out - Ulster: A Ward (ankle), J Williams (knee), S Coulter.
Munster: D Wallace, A Horgan, P O'Connell, M Cahill.
POOL A - NEATH v EBBW VALE (at the Gnoll, 6.45pm).
Despite falling to Ulster last weekend, Neath are in a rich vein of form, and with three wins in this years Celtic League, the Welsh All Blacks will start this match as hot favourites.
But Neath coach Lyn Jones is keeping his feet firmly on the ground
"Over the last four years we have had some great high scoring matches against them, and the moment you take a win for granted you will lose."
Neath won both meetings in the Welsh/Scottish League, but Vale were victorious in the Principality Cup last season. The Steelmen have only won twice in Welsh League games at the Gnoll, 16-15 in 1996/97 and 22-20 in 1998/99.
Ebbw Vale have recorded just one victory in the Celtic League this season, against Caerphilly.
Peter Sidoli, younger brother of Pontypridd lock Robert, is impressing after sitting most of last season out with injury.
Coach Mike Ruddock had words of support for the young forward. "Peter [Sidoli] made things happen on Saturday," he said
Ruddock has included flanker Paul Williams at openside flanker with Tyron Morris suffering from a neck injury. Willaims recent memories of the Gnoll include a sending off last season, so he will be keen to make up for that this weekend.
Neath: (from) Backs - G Morris, J Story, D Tieuti, A Bateman, S Williams, L Jarvis, S Marsden, S Connor, A Moore, P Horgan. Forwards - D Jones, A Jones, A Millward, S Jones, B Williams, G Llewellyn (capt), A Newman, H Jenkins, S Martin, A Mocelutu, S Tandy, N Bonner-Evans.
Ebbw Vale: R Davies; N Wakely, M Ridley, E Binham, R Shorney; M Meenan, B Shelbourne; P Jones, J Evans, A Black (capt), P Sidoli, N Edwards, K Tuipulotu, W Thomas, P Williams, Replacements: C Gay, K Crawford, O Booyse, R Williams, A Bevan, S Mitchell, A Takarangi.
Referee: G Davis (Scotland).
Out - Neath: B Sinkinson (knee), J Leyshon (shoulder), A Matthews (knee).Ebbw Vale: C Billen (back), D Penisini (knee), T Morris (neck), P Matthews (ankle)
Previous meetings: In Welsh league matches Neath lead 9-7 on wins overall
and by 6-2 at home.Last season: Neath won 45-6 away and 50-8 home in league matches, but Ebbw Vale won 20-10 at home in the Principality Cup Round Seven.
Form guide: Ebbw Vale's only league wins at the Gnoll were by 16-15 in
1996/97 and 22-20 in 1998/99.
POOL A - EDINBURGH RUGBY v LLANELLI (at Meadowbank, 7.30pm).
Llanelli take their strongest available side to Scotland hoping to break their Meadowbank duck. The Scarlets have lost all three previous games Edinburgh's home stadium.
Scarlets coach Gareth Jenkins makes three changes from the side that beat Ebbw Vale 37-25 last weekend. Wales trio Stephen Jones, Iestyn Thomas and Robin McBryde come in for Gareth Bowen, Phil John and Marcus Thomas at fly-half, prop and hooker respectively.
Simon and Guy Easterby are unavailable for selection as they are included in Ireland's squad for the World Cup qualifier against Georgia in Dublin.
Jenkins says his Scarlets have to win all their remaining matches, and with Edinburgh pushing for top spot in Pool A, this will be no easy task.
Jenkins knows the Scarlets must raise their game in order to win.
"We are going up a class when we play these teams (Irish and Scottish) but that brings the best out of Llanelli."
Edinburgh: (not yet available)
Llanelli: G Evans; M Jones, M Watkins, L Davies, S Finau; S Jones, D Peel; I Thomas, M.Thomas, M Madden, V Cooper, L Gross, D Jones, D Hodges, I Boobyer. Replacements: J Davies, M Thomas, C Wyatt, L Cudmore, M Phillips, G Bowen, M Cardey.
Referee: S McDowell (Ireland).
Out - Edinburgh: M di Rollo (knee).
Llanelli: N Boobyer (foot fracture); S Easterby & G Easterby (on Ireland duty), S Quinnell (nose), D Williams (knee).
Welsh/Scottish League wins: Three each with neither side winning an away
Last season: Llanelli 42 Edinburgh 17; Edinburgh 40 Llanelli 8.
POOL B - BORDERS v LEINSTER LIONS (at Netherdale, 7.30pm).
Celtic League champions Leinster are desperate for a victory to turn their campaign around.
A defeat to Borders would surely end all hope of quarter-final qualification. The Lions beat the Scottish Borders in the 1996/97 Heineken Cup 34-25, and a repeat performance will take the pressure off coach Matt Williams, who has come under increasing criticism from a Leinster public used to success.
The Borders will be without wings Shaun Longstaff (groin) and Cammie Murray (shoulder), and are desperate for a change of luck.
They have lost three matches by a combined total of five points, including last weekend's heartbreaking one point loss to Pontypridd.
Borders: T Vili; N Walker, K Utterson, J Stuart, C Moir; G Townsend, G Armstrong (capt); P Thomson, S Scott, B Douglas, D Weir, R Metcalfe, C Feather, S Sititi, M Taylor. Replacements: S Paterson, C Laidlaw, I Fairley, A Rennick, C Stewart, C Dunlea, S Gunn.
Leinster: C Warner; J McWeeney, K Lewis, S Horgan, G D'Arcy; A Dunne, B O'Meara; E Byrne, P Smyth (capt), N Treston, B Gissing, B Kearney, D Dillon, V Costello, L Toland. Replacements: P Coyle, G Hickie, A McCullen, S Jennings, S Keogh, M Leek/G Browne, D Quinlan.
Referee: H Watkins (Wales).
Out - Borders: S Longstaff (Groin), C Murray (shoulder), G Morton (shoulder),
G Graham (calf), S Cranston (ankle).
Leinster: N Spooner, P McKenna, A Magno, E Miller, B Willis, B O'Riordan.
Previous meetings: In the 1996/97 European Cup, Leinster won away 34-25.
A special video package as Pontypridd claimed the double for the first time in their history by winning the Principality Premiership final, including match build-up, highlights, post match reaction and dressing room celebrations.