With only two points separating the top three sides, a loss for any of them could end their dreams of hoisting the sought-after trophy in the middle of May.
This Friday night, the Scarlets host the Leinster Lions at Stradey Park and will be desperate to erase the memories of last weekend's Heineken Cup quarter-final loss to Biarritz Olympique at the same venue.
Ulster host fellow Irish province Connacht - who have proved to be a headache for many more-fancied teams this season - as they try to keep the Celtic League trophy in Ireland after wins by Leinster and Munster in the previous two seasons.
The Dragons put their unbeaten League home record on the line when they welcome the Cardiff Blues to Rodney Parade in a crucial game for both sides.
And the excitement isn't just centred on the race for the title. With Heineken Cup spots up for grabs among the Welsh and Scottish sides, things are getting tight at the other end of the table. The bottom-placed side from both Wales and Scotland lose their place in Europe's top tournament next season, and the heat is going on several teams with only four matches left to play.
The Blues are holding down the fifth Welsh position - they are currently the ones in most danger of failing to qualify for the 2004 / 2005 Heineken Cup - with 42 points, but have the Neath-Swansea Ospreys (45) in their sights, while the Celtic Warriors (48) are having a nervous look over their shoulders.
The Blues have the daunting task of getting four points at Rodney Parade - which has proved beyond any Celtic team this season - while the Ospreys host bottom-placed The Borders and will be gunning for the full five points.
The Warriors face a tricky trip to Glasgow on Friday night, with the Scottish side determined to stay above The Borders to keep their Heineken Cup spot next season.
In the other game, defending champions Munster take on the leading Scottish side and Heineken Cup quarter-finalists Edinburgh Rugby at Musgrave Park as they build towards a mouth-watering Heineken Cup semi-final against London Wasps.
All in all, it's a bumper weekend of Celtic rugby as the leading teams realise that one slip could end their chances of winning the title they've spent the season chasing - and others go in search of the points to boost their hopes of making the cut for Heineken Cup places next season.