The haemodynamic effects of nifedipine, propranolol, and the combined administration of the two drugs were studied in 12 patients with hypertrophic obstructive cardiomyopathy. The combined administration of nifedipine and propranolol appeared to be superior to that of nifedipine alone. The spontaneous heart rate was reduced in most cases after nifedipine plus propranolol, and at atrial pacing the following results were obtained: left ventricular peak systolic pressure was reduced from 200 +/- 39 to 157 +/- 30 mmHg; a positive correlation was found between the pre-drug left ventricular end-diastolic pressure and the magnitude of reduction in left ventricular end-diastolic pressure; systolic blood pressure was reduced from 125 +/- 31 to 111 +/- 27 mmHg, and total peripheral resistance was reduced from 1403 +/- 307 to 1160 +/- 209 dyne s-1 cm-5. The combined administration reduced the resting left ventricular outflow gradient from 76 +/- 19 to 45 +/- 26 mmHg, while cardiac index was left unchanged. The effects on mean pulmonary arteriolar resistance and mean pulmonary arteriolar resistance and mean pulmonary capillary venous pressure were in most cases slight and insignificant. The results indicate an improved haemodynamic condition in patients with hypertrophic obstructive cardiomyopathy after the combined administration of nifedipine and propranolol: a treatment that might provide a new and useful alternative to already existing medication.