Summary. Immunocytochemical study was performed in the Bufo marinus retina to reveal the localization of y-aminobutyric acid (GABA)-immunoreactivity in neuropeptide Y (NPY)-, substance P (SP)-, serotonin (5HT)-and tyrosin hydroxylase (TH)-immunoreactive amacrine cells. GABA-immunoreactivity was present in all NPY-, in some of the SP-and 5HT-containing amacrine cells, but not in TH-immunoreactive amacrine cells. Among the 5HT-immunoreactive amacrine cells, a population of 5HT-synthesizing and most of the 5HT-accumulating cells were GABA-immunoreactive. These results indicate that neuropeptide-and GABA-immunoreactivity are colocalized in amacrine cells of the anuran retina. We propose a possible co-transmission for two classical neurotransmitters (GABA and 5HT) in some of the 5HT-containing amacrine cells.Previous studies have indicated that the y-aminobutyric acid (GABA)-ergic amacrine cell population is morphologically (POURCHO and GOEBEL, 1983;YANG et al., 1991) and immunohistochemically (VERSAUX-BOTTERI et al