The expression patterns of inwardly rectifying potassium (Kir) channel subunits (Kir 1.1, 2.1, 2.3, 3.1, 3.2, 3.3, 4.1, and 4.2) were studied in rat retina by immunohistochemistry, with special emphasis on neuronal expression. Except for Kir4.1, the subunits tested were all expressed on neurons in the inner nuclear and ganglion cell layers. While Kir2.1 was densely present in the cytoplasm, the staining for all other subunits was predominantly expressed on the cell membrane. Most subunits, but not Kir 2.1 and 2.3, were present in the outer and inner plexiform layers to different extents. Kir4.1-immunoreactivity was found in astrocytes wrapping retinal blood vessels, in addition to the Müller cell endfoot. The differential expression of the Kir subunits suggests the diversity of physiological roles these channels may play.