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

Effect - Code
Full health - health
Invisibility - invisible 1
Disable invisibility - invisible 0
Full ammunition - ammo
Flight mode - fly
No clipping mode - ghost
Disable flight and no clipping modes - walk
Freeze enemies - playersonly
No enemies - killpawns