JUSTIN BAILEY refers to a famous Metroid password that gives the player nearly all the power-ups needed to beat the game, and allows the player to use Samus in a purple leotard rather than her armored suit.

A great deal of speculation surrounded the password. For instance, Justin Bailey was originally thought to be one of the creators of the game, but no such name appears in the game credits. Some have said Justin Bailey was the winner of a contest held by Nintendo of America, and his prize was having his name be in the game. It is also often said that the Justin Bailey code was a reference to an English or Australian term for a bathing suit. Allegedly, bathing suits are referred to as "bailies," so "Justin Bailey" would more accurately be rendered as "Just In (a) Bailey" or "Just In a Swimsuit," which is what Samus appears to wear when the code is used. However, no such slang for bathing suit actually exists.





NARPAS SWORD, a recently discovered code was purposefully built-in to the game
This code gives Samus infinite health and missiles, the Ice Beam, and every power-up in the game with the exception of Energy Tanks, Missile Expansions (both of which are unnecessary with this password) and the Wave Beam (Samus cannot carry both the Ice and Wave Beams simultaneously). The player must still find and defeat both mini-Bosses and the Mother Brain.

When this password is used, the Ice Beam's projectiles are represented by a different sprite than is used during regular gameplay or when using the "JUSTIN BAILEY" password. The sprite is the same one used to make up Samus' Wave Beam only rendered in a different color.

There have been small debates on what the password stands for. Some think it refers to a "Narpas" sword, Narpa's Sword, or possibly even Narpas's Word. Others feel the password is properly read as "NAR Password," with several suggestions having been offered for the meaning of "NAR": an abbreviation for the name of the person who designed the password system (Tohru Narihiro); an acronym for "North American Release"; or an acronym for "Not A Real", as in "Not A Real Password".