Cardiac catheterisation with pressure measurements, left-ventricular cine-angiography and selective coronary angiography confirmed the diagnosis of hypertrophic obstructive cardiomyopathy in 20 patients. After a mean observation period of 20 months during which most of them were treated with beta-blockers, verapamil, 480 mg by mouth, was given for an average of 12 months. There was an impressive improvement in symptoms, compared with the state under beta-blocker treatment. There was a significant reduction in the ECG signs of left-ventricular hypertrophy and of the radiologically measured heart volume. Treatment of this condition with verapamil appeared to be superior to that with beta-blockers.