1. The therapeutic efficacy of papaverine for tardive dyskinesia was tested in 23 psychogeriatric and 18 chronic schizophrenic patients. Papaverine was given in slow-release capsules at 150 mg BID for one week followed by 300 mg BID for five weeks. A single blind design was used with blind raters and a 6-week no drug control condition. 2. Oro-facial dyskinesia was significantly reduced by papaverine in the psychogeriatric group during the first six weeks. Only a few patients showed at least 50% improvement of dyskinesia scores. Overall the drug effects were modest. 3. Other findings of interest were a) EEG showed increased per cent time of alpha and reduced beta 1. b) Parkinsonian side effects tended to confirm dopamine antagonism by papaverine. c) No tolerance was seen after six weeks. d) Elderly female patients and those with oro-facial dyskinesia appeared to respond best to papaverine.