There has been considerable debate whether the opsin genes of several 'blind' animals code for functional photopigments, and if so, what physiological responses these photopigments may mediate1. We report the first isolation and in vitro expression of a functional cone-like photopigment from the highly degenerate eye of a visually blind fossorial mammal, the blind mole rat (Spalax ehrenbergi). Furthermore, we show that this photopigment mediates the effects of light on circadian behavior in this species.