The antihypertensive and haemodynamic efficacies of ketanserin and ketanserin plus enalapril were compared. The monotherapy phase of the study involved the oral administration of 40 mg ketanserin twice daily or 20 mg enalapril once daily for 12 weeks to 25 hypertensive patients. Systolic and diastolic blood pressures were significantly reduced by both drugs. Left ventricular function both at rest and during effort improved significantly with either drug. This was due to a reduction of end-systolic volume; end-diastolic volume decreased only with the use of enalapril. Combination therapy, involving 16 patients and both drugs given at the original dosage schedule for 12 weeks, resulted in further reductions in systolic and diastolic blood pressures, and an improvement in left ventricular function; indices of diastolic function were not modified. In conclusion, ketanserin and enalapril showed comparable antihypertensive and haemodynamic activities. A combination of ketanserin and enalapril increased the favourable characteristics of both drugs.