1. The dose-peak effect relationship of lisinopril was evaluated in a double-blind, parallel study in 83 patients with mild to moderate essential hypertension (supine diastolic blood pressure = 95-115 mm Hg). 2. After a 4 week placebo washout, patients were randomly assigned to one of four treatments: lisinopril 2.5, 10, 20 or 80 mg day-1 for 1 week. 3. Lisinopril 10 and 20 mg day-1 produced similar peak antihypertensive effects which were greater than that produced by 2.5 mg day-1, but less than that of 80 mg day-1. If the incidence of first-dose symptomatic hypotension is related to the peak effect, then an initial lisinopril dose of 20 mg should not pose any greater risk than a 10 mg dose. 4. The magnitude of antihypertensive response at 24 h postdrug appeared to be dose related across the 2.5 to 80 mg day-1 range.