This study describes for the first time the presence and distribution of the nitric oxide (NO) synthesizing enzyme, NO synthase (NOS), in the retina of a teleost. NADPH diaphorase (NADPHd) histochemistry and NOS immunohistochemistry revealed both NOS immunoreactive and NADPHd positive structures in photoreceptor outer segments, amacrine cells, horizontal cells and ganglion cells. Since NO is known to stimulate the synthesis of cGMP, our results implicate an important role for NO in retinal function, especially in cGMP related events in the photoreceptors.