Benzodiazepines have several advantages over other antidyskinetic drugs in treating tardive dyskinesia. The authors conducted a controlled study of clonazepam versus the active placebo of phenobarbital in 21 psychiatric patients with tardive dyskinesia. Both drugs significantly reduced dyskinetic movements: clonazepam had a stronger effect on orofacial dyskinesia, and phenobarbital was more effective for limbs and axial movements. Clonazepam was also more effective for drug-free patients and those receiving low doses of neuroleptics than for all patients given phenobarbital and for clonazepam patients taking high doses of neuroleptics. The authors suggest that future treatment studies focus on the effects of antidyskinetic drugs on distinct body regions.