The present study describes the patterns of NADPH-diaphorase reactivity in the ventral and dorsal lateral geniculate nuclei of rats. In the ventral lateral geniculate nucleus, two distinct populations of NADPH-diaphorase reactive cells are apparent. One population is deeply stained, generally larger in somal size and located in the more superficial or dorsolateral regions of the nucleus. The second population of reactive cells in the nucleus is lightly labeled, small in somal size, and found in deeper or more ventromedial regions of the nucleus. Double labeling with an antibody to GABA revealed that neither cell class is GABAergic. In the dorsal lateral geniculate nucleus, reactivity is apparent in lightly labeled small cells only, most of which are GABA immunoreactive also. The NADPH-diaphorase reactive cells, however, form only a small proportion of the total population of GABAergic cells in the nucleus. The striking feature of the NADPH-diaphorase reactive cells in the dorsal lateral geniculate nucleus is their spatial distribution. Most cells are located in the more superficial or dorsolateral areas: very few are apparent in deeper or more ventromedial areas of the nucleus. This distribution closely parallels the location of the outer "shell" region of the nucleus (see Reese, 1988), which receives most of its afferents from the smaller class II and III ganglion cells of the retina and from the superior colliculus.