RETINAL γ-aminobutyric acid type C (GABAC) receptors are believed to consist of ρ subunits. The pharmacological properties of GABACreceptors appear to vary among different species. Since the mouse is an important model for gene targeting and behavioral studies, this study was aimed at cloning ρ subunits in the mouse. Here we report the isolation of two full length cDNAs corresponding to mouse ρ1 and ρ2 subunits. In contrast to the rat, both subunits in mouse are able to form homomeric receptors, but only ρ2 receptors are insensitive to picrotoxinin. Mouse ρ1 and ρ2 also co-assemble to form heteromeric receptors. These findings form the basis for further study on GABACreceptors using the mouse model.