Welsh Domestic rugby's biggest day of the season will see more than 55,000 spectators at the Principality Stadium for Judgement Day V.
It's a last chance for players to impress British and Irish Lions selectors before coach Warren Gatland names his squad on 19 April.
And with all four regions in action, Wales summer tour coach Robin McBryde has said performances could have a major impact on squad selection.
So what's at stake and who can impress the selectors? Here's a quick guide to the two matches.
Cardiff Blues v Ospreys (14:45 BST)
There is more hanging on this one for third-placed Ospreys than the Blues.
The Swansea-based region were looking safe in the Pro12 play-off places until losing their last two matches away at bottom club Treviso and at home against leaders Leinster.
The 11 point buffer they enjoyed over the team in fifth-place before those results is now down to two, with Ulster and Scarlets breathing down their necks.
Ospreys' two remaining matches after Saturday are against their main play-off rivals so they need a win to keep control of their own fate.
At least Steve Tandy's men don't have to worry about European qualification, having already secured a place in the 2017-18 European Champions Cup.
Cardiff Blues will face a play-off for a place in European rugby's top flight - even if they overtake sixth-placed Glasgow Warriors.
Qualifying rules mean at least one team from each of the five participating countries qualifies, so Glasgow will take Scotland's place with Edinburgh marooned in ninth place.
Revenge and pride may be motivating factors for Danny Wilson's team after they were thrashed by Ospreys in their previous meeting this season.
Previous meeting: Ospreys 46-24 Cardiff Blues, 7 October
Last season: Cardiff Blues 27-40 Ospreys
Lions watch: With Dan Biggar sidelined keep an eye on Rhys Webb and Justin Tipuric of the Ospreys. With Sam Warburton out of action, it's difficult to see any of Saturday's Blues line up making the trip.
Wales tour bolters: Olly Cracknell of the Ospreys and Blues wing Rhun Williams.
Newport Gwent Dragons v Scarlets (17:15 BST)
Scarlets are hot on the heels of Ospreys and will overtake their west Wales rivals if they beat the struggling Dragons and Ospreys slip-up against the Blues.
Dragons make a habit of playing well against their Welsh rivals, however, and could have won at Parc y Scarlets earlier this season.
But current form suggests another win for Wayne Pivac's team as they strive for a place in the end-of-season play-offs by securing a top-four finish.
With a difficult trip to Connacht and a final day showdown at home against Ospreys to come, Scarlets would like to get the points in the bag.
Kingsley Jones' Dragons have lost nine consecutive matches, culminating in Saturday's 29-14 defeat by Zebre in Parma.
They can finish ninth in the table, but will have an anxious eye on Zebre who are just two points behind them in 11th place.
Previous meeting: Scarlets 31-27 NG Dragons, 8 October
Last season: NG Dragons 20-34 Scarlets
Lions watch: Plenty to watch in the Scarlets line-up. Jonathan Davies, Scott Williams, John Barclay, Ken Owens, Liam Williams and Rob Evans are potential candidates.
Wales tour bolters: Rhys Patchell, James Davies and Steff Evans for Scarlets. Cory Hill for the Dragons.