There are five matches this evening, the pick of the ties being the visit of Munster to Stradey Park. The Irish side has been off the pace of the leaders all season, and this match could be a make-or-break game for them. If they slip any further behind the front-runners, their Celtic league season could be effectively over.
The Scarlets have lost two matches in a row, a rare occurrence for Gareth Jenkins' men. They will be desperate not to lose further ground as they have slipped to third place in the league.
There is an all-welsh derby at St Helens as the Dragons front up to face the Ospreys. Despite the Dragons being in second spot, this one could come down to passion, write off Lyn Jones' side at your peril.
The Celtic Warriors have a tricky game against Leinster Lions at Lansdowne Road.
Tomorrow, the resurgent Cardiff Blues have an away day in Connacht. The Blues lost to the Irish side earlier in the season at the Arms Park, and will be looking to avenge that loss.