Pontypridd travel to Stradey Park where they managed a 13-13 draw in the league earlier in the season. Ponty appeared in two of the last three finals and they may put a stop to the Scarlets who are chasing their 19th final appearance.
Maesteg are having a tough time in the league and will welcome the respite of not playing for league points. The Wanderers have just recovered their form after a four-match losing run and will be favourites to go through at Llynfi Road.
Swansea will not relish a trip to the Gnoll to face a Neath side who are clear leaders of the Principality Premiership. The Welsh All-Blacks have already beaten the All-Whites this season and it will be a major shock if they fail to take advantage of being at home.
There is sure to be at least one minnow in the draw for the fifth round as Old Illtydians of League Three South East play host to Tondu of League Three South West. The lowest-placed side in round four is Glynneath of League Four South West. They have already beaten Rhyl, Penarth and Bedlinog in earlier rounds and have yet to concede a try but Narberth of League One West will give their defence a stern test and leave them to concentrate on gaining promotion.
Carmarthen Quins will be confident of pulling off a shock against last season's beaten finalists Cardiff, while Merthyr entertain a Cross Keys outfit that has been very inconsistent so far this season. Bedwas could find that their trip to Bonymaen ends in defeat, Newport should go through against Llanharan of League One East at Rodney Parade, and Ebbw Vale can make full use of home advantage to knock out Caerphilly.