First person perspective
Press Down, Up, L, B, Z, Left, C-Up, C-Right, C-Left, Z when "Press Start" appears at the opening screen. (A tone confirms correct entry.)

Freeze thrower with unlimited ammunition
Press Down, Up, A, L, R, Z when "Press Start" appears at the opening screen. (A tone confirms correct entry.)

Rifle with unlimited ammunition
Press C-Up, C-Down, C-Left, C-Right, L, R when "Press Start" appears at the opening screen. (A tone confirms correct entry.)

Character set 5
Press Right, B, Left, L, A, Z when "Press Start" appears at the opening screen. (A tone confirms correct entry.)

Character set 6
Press Up, Down, B, A (x2), Left when "Press Start" appears at the opening screen. (A tone confirms correct entry.)

Flat shade map
Obtain all secrets in the secret level, "Wetworld".

Weather
Obtain all secrets in Level 6: Under Siege.

Maximum blaster ammunition
Slay all opponents in Level 9: Jailbreak.

Maximum shotgun ammunition
Rescue all babes in Level 10: Up Ship Creek.

Maximum rifle ammunition
Rescue all babes in Level 11: Ft. Roswell.

Maximum revolver ammunition
Rescue all babes and obtain all secrets in Level 12: Probing The Depths.

Maximum sawn-off shotgun ammunition
Slay all opponents in Level 13: White Chapel Killings.

Maximum SMG ammunition
Obtain all secrets in Level 15: Dawn of the Duke.

Maximum gattling gun ammunition
Slay all opponents in Level 16: Hydrogen Bomb.

Maximum Volt-C ammunition
Obtain all secrets in Level 17: The Rack.

Maximum sniper ammunition
Rescue all babes in the secret level, "Going Down".

Maximum gamma ammunition
Rescue all babes in Level 21: Alien Mothership.

Maximum freezer ammunition
Slay all opponents in Level 20: The Brothers Nukem.

Secret level: Going Down
Obtain all of the time machine pieces before reaching the rack. A second portal should appear in a room adjacent to the first.

Secret level: Wetworld
After powering up at the end of level 3: Nuclear Winter, jump onto the roof below. (You will see a Medkit there.) From the roof, jump into the water and swim to the floating platform.

Big head mode
Rescue all babes in Level 2: Liberty or Death.

High speed zombies
Rescue all babes in Level 8: Dry Town.

Ice skin
Rescue all babes in Level 5: Fallout.

Additional characters in multi-player mode
Complete any level and save the game to unlock an additional character in multi-player mode.

Action Nuk'em mode
Press Down (x2), A, Z (x2), Left, A when "Press Start" appears at the opening screen. (A tone confirms correct entry.)
Alternately, successfully complete the game.

Character set 1
Press A, L, R, Left, B, Down, Up when "Press Start" appears at the opening screen. (A tone confirms correct entry.)

Extreme mode
Successfully complete the game with all babes rescued and all opponents killed.

Character set 2
Press B, A (x2), R, L when "Press Start" appears at the opening screen. (A tone confirms correct entry.)

Big gun mode
Slay all opponents in Level 3: Nuclear Winter.

Character set 3
Press L (x2), Up, Down, R, B, A when "Press Start" appears at the opening screen. (A tone confirms correct entry.)

Character set 4
Press B (x3), R, Left, A when "Press Start" appears at the opening screen. (A tone confirms correct entry.)