Locate the tunnel in the Freeway level. There is a large box on one side of the tunnel. Jump on top of the box, and from there jump on to the ledge. On the far side of the ledge there is a pair of night vision goggles. Jump a little bit above the goggles to enter the vents of the L.A.R.D. Police station. Use the night vision goggles, and follow the air ducts and shoot through the fan on the right side of the wall; or keep going and break the second fan that also on the right side of the wall. Duke may now explore the interior of the L.A.R.D. Police Station.
Energy refill
Destroy any water source, including fountains, fire hydrants, and toilets. Stand in the water and hold A to slowly restore energy. Alternately, stand in front of a toilet or urinal and press A.
Tiny Duke
Start a game in co-op or deathmatch mode. Enable the "All Items" code, as well as the "Friendly Fire" option. Have one player shoot the other player with the shrink weapon. Enable the "Invincibility" code, then disable "Invincibility" to get a small version of Duke. Note: Weapons can not be used in this state.
Huge Duke
Start a game in co-op or deathmatch mode. Enable the "All Items" code, as well as the "Friendly Fire" option. Have one player shoot the other player with the expander weapon. Enable the "Invincibility" code before the first player explodes, then disable "Invincibility".
Unlimited jet pack fuel
Enable the "All items" code while flying with the jet pack.
Level select
Enable the "Cheat mode" code. Press L(3), C-Right, Right, Left(2), C-Left in the NTSC version of the game. A level select option will now be available. For the PAL version of the game, press R, L, R, C-Down, Right, Up, Left, C-Up.
No monsters
Enable the "Cheat mode" code. Press L, C-Left, Left, R, C-Right, Right, Left(2), Right in the NTSC version of the game. The sound of a siren will confirm correct code entry. Monsters may now be toggled on the cheat menu. For the PAL version of the game, press L, C-Up, Left, L, C-Down, R, L, R.
Invincibility
Enable the "Cheat mode" code. Press R(7), Left at the main menu in the NTSC version of the game. A sound will confirm correct code entry. The invincibility option may now be enabled on the cheat menu. For the PAL version of the game, press R, C-Right, R, L, R(3), Left.
All items
Enable the "Cheat mode" code. Press R, C-Right , Right, L, C-Left , Left, C-Right, Right at the main menu in the NTSC version of the game. For the PAL version of the game, press R, C-Right, Down, L, C-Up, Left, C-Right, Left.
Cheat mode
Press Left(2), L(2), Right(2), Left(2) at the main menu to access the cheat menu in the NTSC version of the game. For the PAL version of the game, press Left, Down, L(2), Up, Right, Left, Up.
Immortal
In the cheatmenu key in R(7x), left. If you did this alright, you will hear a sound.
Unlimited jetpack
Execute the All items code while you are flying with the jetpack.
All items
In the cheat menu, key in R, C-right, right, L, C-left, left, C-right, right.
Cheat mode
Key left (2x), L(2x), Right(2x), Left(2x) in the main menu to go into the cheat menu.
Monsters On/Off
Enter the cheat menu code then enter this code: L, C-Left, Left, R, C-Right, Right, C-Left, C-Left, Left
Level Select
Enter the cheat menu code and then enter this code: L, L, L, C-Right, Right, Left, Left, C-Left.
Hear Butthead's voice
Begin game play on the Duke Burger level. Locate the drive thru sign on the outside of the building. Approach the "Order Here" sign and press A or move around to the center and back of the sign and press A. Butthead's will say "Go away. We're like closed".
Big, small, midget dukes
For big: use expander on target and just before it explodes, put on invinsibility and back off and it will be big.
For midget: repeat "for big" and just use the shrinker.
For small: (permanent) use shrinker and put on invinsibility and back off and voila!
