In response to light, most retinal neurons exhibit gradual changes in membrane potential. Therefore, K⁺ channels which mediate threshold currents are well-suited for the fine-tuning of signal transduction. Using molecular biology techniques, all three members of the ether-à-go-go related gene (erg) K⁺ channel family (Kv11) were found to be expressed in the mammalian retina. The localization of the different erg channel subunits in the mouse retina was investigated by immunofluorescence experiments. M-erg1 displayed the most abundant expression with strongest immunoreactivity in the inner segments (IS) of photoreceptors and in the outer part of the inner nuclear layer (INL), which might comprise postsynaptic regions of ON bipolar cells. In addition, immunoreactivity was found in the inner part of the outer plexiform layer (OPL) and in the inner plexiform layer (IPL). Immunoreactivity for m-erg2 was observed in the outer part of the OPL and throughout the IPL. Double-labeling for vGluT1 indicated a mainly presynaptic localization of m-erg2 and thus its possible involvement in neurotransmitter secretion. No significant staining for m-erg3 was detected in the neuronal retina, but slices from whole eye cup preparations demonstrated a strong erg3 immunoreactivity in the apical membrane of the retinal pigment epithelium (RPE), where erg3 channels could play a role in K⁺ homeostasis or osmoregulation. The present immunohistological results point to different physiological roles of the three erg channels in the mouse retina.