Two players control two soldiers named Ricky and Mary, who must fight their way through large eight-way scrolling levels rescuing their comrades who are being held by aliens. After they have rescued a certain number of hostages the exit opens and they can pass through it in order to fight the end-of-level guardian. If this monstrosity is defeated, they move onto the next stage. As well as two player simultaneous gameplay, Alien Syndrome features pick-ups which assist the player including better weapons and maps of the current level.
[edit]
Ports

In 1988, the game was ported to the Sega Master System, MSX, Amiga, Atari ST, Amstrad CPC, Commodore 64, and Famicom/Nintendo Entertainment System (published by Tengen). Later, the game would be ported to the ZX Spectrum (1989) and the Sega Game Gear (1992).

The game was also ported with updated graphics and sound for the PS2 as part of the Sega Ages re-release program, and included in US version of the Sega Classics Collection (it was removed from the European version to receive a lower age certificate). This version has updated controls, adding the use of both analog sticks, similar to the gameplay seen in Robotron: 2084 and Smash TV. The original arcade game was also included as an unlockable in Sonic's Ultimate Genesis Collection.

A sequel of the same name, Alien Syndrome, was released for Wii and PSP on July 24, 2007.