Valve plans to offer a demo of Left 4 Dead "shortly before release", which is 18th November on Steam and 21st November in shops.
The sampler will "most likely be the first two maps of the hospital campaign", according to comments made by Valve's Chet Falisek to De-Frag.
These missions begin outside in a series of streets, before descending into a subway station that takes players to their next safehouse.
Left 4 Dead is the co-op shooter for PC and Xbox 360 that has friends fight hordes of infected baddies. You might know them as zombies.
The twist is that opposing players can dress up as the Infected in frantic online multiplayer fights, lending baddies all the unpredictability and menace of the tummy squits.
Rush over to our Left 4 Dead gamepage for a silly amount of content probably written by Tom who likes that sort of thing.