Clonazepam and chlordiazepoxide were administered chronically in increasing doses for three weeks in two different strains of mice. Forebrain [3H]diazepam binding was assayed in groups of mice sacrificed at 2, 26, 50 hr and 10 days following the last dose. Scatchard and single point analyses revealed a significant decrease in the number of [3H]diazepam binding sites [Bmax] which persisted for at least two days following chronic clonazepam treatment. The Bmax changes observed following chlordiazepoxide treatment were less pronounced than those elicited by clonazepam. No significant changes in receptor binding affinity (Kd) were detected with either drug. In the clonazepam-treated animals, Bmax values returned to normal by day 10 after drug treatment. Chronic benzodiazepine administration therefore induced a decrease in the apparent number of benzodiazepine binding sites in the mouse forebrain. The magnitude and duration of the observed subsensitivity appears to depend on the potency of the administered benzodiazepine.