BACKGROUND: To determine the efficacy and dose-response of the new angiotensin II receptor antagonist eprosartan, we conducted a 4-week, double-blind, randomized, multicenter study in 114 men with essential hypertension using trough clinic and ambulatory blood pressure measurements.METHODS: Patients were included if the seated diastolic blood pressure was between 95 and 115 mmHg inclusive and 0-12 h diastolic blood pressure was at least 87 mmHg. The effects of twice daily eprosartan at 50, 100, 150 and 200 mg were compared with those of placebo. RESULTS: At trough, the clinic diastolic blood pressure was reduced significantly only by the 200 mg dose compared with placebo (mean placebo-subtracted change -6.0 mmHg, 95% confidence intervals -10.5, -1.5, P = 0.001). In contrast, the 12 h mean reduction in diastolic blood pressure was significant for both the 150 mg dose (mean change -5.3 mmHg, 95% confidence intervals -10.2, -0.1, P = 0.0075) and the 200 mg dose (mean change -5.5 mmHg, 95% confidence intervals -10.3, -0.6, P = 0.0049). Similar trends were observed for the systolic pressure and mean changes in 24 h pressures. Eprosartan significantly reduced adjusted mean daytime (0-12 h after dose) diastolic ambulatory pressure linearly with dose. CONCLUSION: These data demonstrate increased sensitivity of the ambulatory blood pressure over the research clinic blood pressure in evaluating the efficacy of the new antihypertensive agent eprosartan. Additionally, these findings demonstrate that higher doses of this drug will be necessary in future studies.