Twenty-four-hour ambulatory blood pressure monitoring (ABPM) was used to assess the efficacy and tolerability of fosinopril, an angiotensin-converting enzyme inhibitor, in 20 hemodialysis patients (12 men, 8 women; aged 28 to 64 years [mean, 54 +/- 9 years]) with mild-to-moderate hypertension. After a 4-week washout period, during which the lowest possible dry weight was achieved, patients were given fosinopril 10 mg/d orally if their predialysis blood pressure (BP) was greater than or equal to 140/90 mm Hg. If BP was not controlled, the dosage was increased every 2 weeks as needed to a maximum of 40 mg/d. Fosinopril was administered for a total duration of 12 weeks. ABPM was done at the beginning of the study and repeated after 6 and 12 weeks of treatment. Significant changes in mean 24-hour systolic and diastolic BP were seen from baseline to week 12 (from 150.3 +/- 4.8 to 138.2 +/- 3.1 mm Hg and from 95.0 +/- 2.8 to 84.3 +/- 3.1 mm Hg, respectively) (P < 0.0001). significant reductions in mean 24-hour systolic and diastolic BP between baseline and week 6 were noted (from 150.3 < 4.8 to 136.1 +/- 4.8 mm Hg and from 95.0 +/- 2.8 to 82.6 +/- 2.5 mm Hg, respectively). The smoothness of BP control was demonstrated by a trough:peak ratio of 58% for ambulatory systolic BP and 62% for diastolic BP. In addition, at 12 weeks, fosinopril induced a significant reduction in systolic BP load from 66.6 +/- 20.0% to 39.2 +/- 16.5% and diastolic BP load from 67.1 +/- 22.8% to 31.4 +/- 6.6% (P < 0.001). Blunting of the circadian rhythm was noted in all patients at study entry. No significant adverse effects were observed. Findings from the present study suggest that fosinopril, given in the usual doses, is well tolerated and results in smooth BP control in hemodialysis patients with mild-to-moderate hypertension.