This study was performed to re-evaluate the clinical position of prenylamine in the management of angina pectoris. After 1 week withdrawal of all anti-anginal agents, followed by another week of placebo administration, seventeen patients were allocated at random to 6 weeks treatment with either penbutolol 40 mg once a day or prenylamine 60 mg t.i.d. Clinical examination, exercise test and anginal attack rate were recorded every 2 weeks. Both drugs reduced the anginal attack rate. None of the drugs caused a significant increase in maximal workload or a significant change in ST-segment depression. Beside a substantially lower rate-pressure product at maximal comparable workload in the penbutolol group (p less than 0.001), no significant differences were observed between the two drugs. No adverse reactions were reported. From these results one can conclude that prenylamine and penbutolol do not differ in their anti-anginal effect. Therefore we are of the opinion that prenylamine has a place in the therapeutic armamentarium for the management of angina pectoris, particularly in patients where beta-blocking agents are contraindicated or in patients who have experienced side-effects of beta-blocking or calcium-entry blocking agents.