Unfixed retinal tissues of adult Bufo marinus were reacted for NADPH-diaphorase histochemistry that resulted in selective staining of populations of bipolar and amacrine cells. The number of stained bipolar cells in the retina was estimated to be 233,600 +/- 38,900 (mean +/- S.D.). These cells were non-uniformly distributed across the retina with the highest density of 4,308 cells/mm2 along the visual streak decreasing to lowest density of 1,378 cells/mm2 at the dorsal and ventral poles of the retina. The stained bipolar cells represented a morphologically uniform population. The number of labelled amacrine cells in the retina amounted to 3,116 +/- 405 including 251 cells that were displaced into the ganglion cell layer. Labelled amacrine cells were also unevenly distributed; with no stained cells in the retinal centre from where the density increased steadily to 72 cells mm2 in the retinal periphery. NADPH-diaphorase positive amacrine cells were classified on the basis of their dendritic arborization pattern into three morphological types: 1) narrow-field cells both at the periphery and the centre of the retina; 2) wide-field amacrine cells, and 3) amacrines with eccentric medium-sized dendritic field. The results of this study provide evidence for the presence of NADPH-diaphorase containing neurons in the anuran retina. Furthermore, this is the first report on the selective staining of bipolar cells for NADPH-diaphorase in the vertebrate retina.