Abstract. Melanopsin is an unusual vertebrate photopigment that, in mammals, is expressed in a small subset of intrinsically photosensitive retinal ganglion cells (ipRGCs), whose signaling has been implicated in non-image forming vision, regulating such functions as circadian rhythms, pupillary light reflex, and sleep. The biochemical cascade underlying the light response in ipRGCs has not yet been fully elucidated. We developed a stochastic model of the hypothesized melanopsin phototranduction cascade and illustrate that the stochastic model can qualitatively reproduce experimental results under several different conditions. The model allows us to probe various mechanisms in the phototransduction cascade in a way that is not currently experimentally feasible.