The efficacy and safety of sustained-release diltiazem, 200-300 mg once daily was compared with that of captopril, 12.5-25 mg twice-daily, in 100 elderly patients (65-85 years old) with mild to moderate essential hypertension (supine diastolic blood pressure 95-115 mmHg). All patients received placebo for 2 weeks, followed by an 8-week double-blind period, and were randomized to either diltiazem (n = 50) or captopril (n = 50). Their blood pressure was measured at trough level at week 4 immediately before dosing, i.e. 24 h post diltiazem dose or 12 h post captopril dose. Also at week 4, in non-responders, diltiazem was increased from 200 to 300 mg once daily and captopril from 12.5 to 25 mg twice daily to achieve a target supine diastolic blood pressure reduction of at least 10 mmHg or a diastolic blood pressure below 90 mmHg. Supine diastolic blood pressure, at week 8, was significantly (P < 0.001) reduced from 102 +/- 1 to 90 +/- 1 mmHg with diltiazem and from 103 +/- 1 to 89 +/- 1 mmHg with captopril, bringing this parameter within normal limits for both groups. Supine systolic blood pressure was also significantly (P < 0.001) reduced. Target blood pressure was achieved in 68% of patients taking diltiazem and in 70% taking captopril. Distribution of adverse events was comparable in both groups; no significant changes in laboratory or electrocardiographic parameters occurred. Two serious events were reported with captopril: one sudden death and one cerebrovascular stroke. Sustained-release diltiazem once a day is a convenient, well tolerated, first line treatment for hypertension in the elderly, for whom the possibility of using two dose levels allows a close regimen adjustment, 200 mg being recommended as a starting dose.