The capacity crowd will be the largest to watch a European game at the Stoop as the two sides unbeaten in Pool 6 meet in London.
Amlin Challenge Cup Champions Harlequins kicked off their 2011/12 Heineken Cup campaign with victory over debutants Connacht in the opening round before beating Gloucester at Kingsholm the following weekend.
Four-times Champions Toulouse beat the Cherry and Whites in the south of France in their opening tie before collecting their second win of the tournament in Galway.
The last time Harlequins and Toulouse met in the Heineken Cup was back in the 2009/10 season. Guy Noves' side completed the double of Quins in that season, winning 23 v 19 at the Stoop and 33 v 21 at Stade Ernest Wallon.