Victory for the Irishmen at Ravenhill would go a long way towards securing a coveted place in the last eight of the Heineken Cup. They outlasted the Scottish North and Midlands, otherwise known as Caledonia, last weekend and in a pool phase of four games, another win would leave them handily placed to progress.
But for all the hard edges that Ulster traditionally bring to their game - qualities that Tony Russ, the former Leicester coach, will only seek to enhance - Harlequins go in as clear favourites after a thoroughly persuasive start to the season. Six Courage league victories off the reel have left them perched on top of the domestic heap and with their league recruits, Gary Connolly and Robbie Paul, beginning to find their feet, the Londoners are the form contenders for Continental glory.
Connolly and Paul team up in midfield once again tonight, their partnership allowing Will Carling another flirtation with the stand-off duties he so clearly covets. The former England captain may look like a centre with ideas above his station, but Ulster are likely to find the combination of all three playmakers too hot to handle.
Leicester are the other English big guns who begin their campaign tonight and by coincidence, they must also cross the Irish Sea. The Tigers face Leinster in Dublin and even though their most experienced international players, Dean Richards and Rory Underwood, are injured, they will expect to take the points from a side beaten by Llanelli in the opening round of matches.
Their confidence is such that they feel able to rest John Liley, their goalkicking full-back, and replace him with the former Huddersfield League professional, Greg Austin. There is a change at scrum-half, too, where Aadel Kardooni comes in for Austin Healey. The teenager Leon Lloyd gets a run on the left wing in place of Underwood.
Elsewhere, the Pool D "Group of Death" sees Toulouse, the reigning champions, making their first appearance in Milan and Cardiff, last season's runners- up, squaring up to Munster at the Arms Park. The Welshmen remain cautious about their quarter-final chances despite their unexpected victory over Wasps on Sunday. Munster, who also won at the weekend, will ask some serious questions and Hemi Taylor's side face an even stiffer examination in Toulouse at the weekend.