The English artistocrats are unbeaten and lead their nearest rivals, Biarritz Olympique, by four points and will want to put some clear water between themselves and the French side and Irish province Connacht Rugby.
Harlequins scrum half Danny Care, who is one of four try-scorers who have scored three tries in the Pool stages, will be hoping to add to his tally in the back-to-back clashes with Zebre.
The Italian new boys are still looking for their first victory in Europe and play only their third game of Heineken Cup rugby.
The Quins will be hoping their recent record of three wins in their last four away games in the tournament, which included a magnificent victory over Toulouse, will hold them in good stead in Italy.
• Harlequins average five successful penalty goals per game so far this season, a tournament high.
• Zebre average 202 metres gained per game, the lowest in the tournament this season.
• Harlequins have averaged more time in possession than any other side in the tournament so far this season (19: 30).
• Harlequins have won three of their last four away games in this competition, this run including a memorable win over Toulouse last season.