The pharmacodynamics, disposition and hormonal responses to acute intravenous and chronic oral diltiazem treatment were compared in young and elderly hypertensive patients. In elderly patients, supine diastolic blood pressure decreased significantly during the first week of treatment (baseline mean +/- standard error of the mean, 100 +/- 1 to 93 +/- 2 mm Hg) and decreased further during the study to 86 +/- 2 mm Hg at the end of the study. Diastolic blood pressure of the young patients decreased significantly by the third week of treatment (from 104 +/- 2 to 97 +/- 3 mm Hg) and decreased further during the study to 94 +/- 2 mm Hg at the end of the study. Baseline supine systolic blood pressure was greater in elderly than in young patients (167 +/- 5 vs 144 +/- 3 mm Hg; p less than 0.01) and was significantly reduced in the elderly by the fourth week (167 +/- 5 to 154 +/- 3 mm Hg; p less than 0.003), with a significantly reduction sustained throughout the 14-week period. Young patients had little change in systolic blood pressure. Supine heart rate tended to decrease in both groups during the 14-week period. Acute intravenous diltiazem pharmacokinetics determined at the beginning of the study showed that total diltiazem clearance was similar in elderly (13.3 +/- 1.0 ml/min/kg) and young (13.7 +/- 1.9 ml/min/kg) patients as was volume of distribution (4.2 +/- 0.3 vs 4.3 +/- 0.6 liters/kg) and elimination half-life (3.78 +/- 0.19 vs 3.69 +/- 0.23 hours).(ABSTRACT TRUNCATED AT 250 WORDS)