The role of GABA or glycine as an inhibitory neurotransmitter is well established, and GABAergic or glycinergic neurons appear to play an important role in the mammalian retinas. It has been reported that certain amacrine, bipolar, displaced amacrine and ganglion cells are consistently labeled with anti-GABA or anti-glycine antisera in the mammalian retinae so far, and it has been suggested that colocalization of GABA and glycine within the retinal neurons could be common in the mammalian retina by recent immunecytochemical and electrophysiological studies. This study was conducted to localize GABAergic and glycinergic neurons and to define whether GABA and glycine are colocalized within same retinal neurons of the rat retina by immunocytochemical method using anti-GABA and anti-glycine antisera. The results were as follows : 1. GABAergic neurons of the rat retina were amacrine, interplexiform, bipolar, displaced amacrine and ganglion cells, and processes of GABAergic neurons formed dense networks with distinct two bands in the inner plexiform layer. 2. Glycinergic neurons were amacrine, bipolar, displaced amacrine and ganglion cells,and their processes were evenly distributed as dense networks through whole inner plexiform layer. 3. 28.5% of GABA immunoreactive amacrine cells and 9.8% of GABA immunoreactive bipolar cells located in the inner nuclear layer,and 11.9% of labeled neurons located in the ganglion cell layer showed glycine immunoreactivity in the rat retina. These results demonstrate that GABA and glycine, major inhibitory neurotransmitters, are colocalized within certain amacrine and displaced amacrine cells, and a few bipolar cells, and that neurons synthesizing and utilizing both GABA and glycine as their neurotransmitters may play an unique role in the visual processing in the rat retina.