In light of the reported efficacy of clonazepam in treating acute mania, we conducted a retrospective review of clinical experience with this agent in maintenance treatment of patients with bipolar affective disorder. Twenty patients with bipolar affective disorder treated with adjunctive clonazepam were identified. A case vignette and summary data on all 20 patients are presented. Clonazepam had been prescribed, in a manner similar to neuroleptics, as part of the maintenance regimen and/or on an as needed basis for acute exacerbations. In six of 17 patients previously receiving combined lithium and neuroleptic treatment, clonazepam successfully replaced the neuroleptic. Overall, eight patients were rated much improved or very much improved, including three of the five cases initially rated most severely ill. Possible mechanisms and treatment strategies are discussed.