The Yalosians were a spacefaring civilization. They breathed a corrosive mixture of 60% nitrogen, 10% benzene, and 30% hydrogen fluoride. They also could not perceive the red-orange part of the Human color spectrum.

Deep Space 9 hosted the Yalosian ambassador in 2371. Major Kira Nerys was in charge of preparing the quarters for the ambassador. Upon testing the mixture in an empty guest quarters, it was found to dissolve the carpet. After Bashir deflected the blame she seemed to be placing on him, he was about to mention something else about them when he was interrupted by an explosion at Garak's Clothiers. (DS9: "Improbable Cause")

This species was only mentioned in dialogue.
According to, the Yalosians hailed from a conjectural planet or star system named Yalosia.
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