The therapeutic value of prenylamine in angina pectoris was tested in two ways. Fourteen patients received 270 mg. of prenylamine per day for one month. This was preceded and followed by one month of placebo therapy. Assessment was made, first by twice-monthly treadmill exercise tests, and secondly by daily records of anginal attacks and nitroglycerin usage. The occurrence of pain and electrocardiographic changes during treadmill exercise was apparently uninfluenced by the drug. However, there was a reduced incidence of spontaneous angina and nitroglycerin usage during the month on prenylamine by contrast with either month on placebo (p <0.05).