1. We studied the binding of [3H]muscimol to membrane preparations of the retina of rabbit (Lepus cuniculus) and turtle (Pseudemys scripta elegans). 2. In both species, [3H]muscimol binding was maximal at 0 degrees C and decreased with increasing temperature, it was saturable, protein concentration dependent and specific. Muscimol, GABA and bicuculline were the most effective displacers, whereas baclofen and diaminobutyric acid were ineffective. 3. In the turtle retina, Scatchard analysis indicated the presence of a single site with a KD of 20.81 nM, and a Bmax of 3.620 pmol/mg prot. 4. In the rabbit, a single site could be identified in the nanomolar concentration range (KD of 12.8 nM, Bmax of 1.327). A study of the association rate of [3H]muscimol binding revealed a faster kinetics in turtle, as compared to rabbit.