Cheat mode:

Press [Enter] to display the console window, then enter one of the following codes to activate the corresponding cheat function.

csmilton - Enable cheat keys
csstigmata - Medlab pass
csitems - Medlab pass
csshroud - Full armor and health
cshealth - Full health
csrosary - Items
csammo - Ammunition
csguns - All guns
csyhwh - God mode
csessence - Give you unlimited essense
cshalt - Stops time
cswire - Makes a traced outline of the game's 3D environment
csvanish - All enemies are gone
cshost - No gravity
csportal - All doorways highlighted yellow

Unknown Effects:

csmapper
cstime
cshide
csback
cs3dnow!on
cs3dnow!off
csunsqueeze
cssqueeze
csuntrace
cstrace
csunframe
csframe2
csframe
csclipmouse
csblah
csverbose
csnotimeouts
cstimeouts