Thirty-seven patients with hypertrophic cardiomyopathy were treated with verapamil in a dose of 240-360 mg/day and followed for 40 months. Marked symptomatic improvement (by at least one class according to the NYHA classification) occurred in 21 (57%) of the patients improved. An increase of left ventricular end-diastolic dimension and volume was recorded. A significant reduction of isovolumic relaxation period (peak velocity of filling and peak velocity of circumferential fibre changes in diastole) occurred. These favourable effects were, however, no longer unequivocal from the fourth month of treatment onwards. Verapamil treatment in hypertrophic cardiomyopathy is a valuable approach by which symptomatic improvement and a favourable effect on some left ventricular functions can be achieved. Its value is, however, to some degree reduced by the lack of long-term effect.