The distribution of GABA receptors in the cerebellum is not homogeneous. In comparison with detergent-treated membranes from the whole tissue the number of [3H]muscimol binding sites per mg protein (Bmax) is about doubled in preparations enriched in large fragments of the cerebellar glomeruli, and it is about one-third in the dissected deep nuclei. On the other hand, the apparent affinity (Kd) is similar in the different preparations. Comparison of the results with earlier studies suggests a heterogeneity in cerebellar GABA receptors and/or their control.