Abstract In earlier electrophysiological experiments on the Mongolian gerbil ( Meriones unguiculatus) evidence was obtained to suggest that the retina of this rodent contains only a single type of cone. The cones were found to have peak sensitivity of about 493 nm. Gerbil rods have peak sensitivity of about 500 nm, yielding a Purkinje shift that is small in magnitude and reversed in direction from that conventionally found among mammals. In a series of experiments we extended electrophysiological and behavioral measurements to include UV stimulation and this reveals a second photopic mechanism. Several pieces of evidence suggest this second mechanism is a cone having peak sensitivity of about 360 nm. Results from adaptation experiments show that the sensitivities of the two cone mechanisms can be independently manipulated, and thus they presumably reflect the operation of two types of cone photopigment. The results from behavioral experiments verify that the gerbil UV mechanism provides information that can be used to make visual discriminations based on intensity differences. A test of color vision additionally suggests that the two cone pigments can support some color discriminations.