Repeated blood pressure recordings by non-invasive devices are of better predictive value than single measurements in the evaluation of antihypertensive treatment. Such a method has been used to establish the dose-effect relationship of perindopril. After a two-week placebo run-in period, 40 patients with essential hypertension (age 56.6 +/- 1.5 years, 31 males, nine females) were treated with placebo or 2, 4 or 8 mg of perindopril once daily for one month following a randomized double-blind design. They were included if at least 75% of diastolic blood pressure recordings, made over an 8 h diurnal period using an automatic blood pressure recorder, were greater than 95 mmHg on placebo. Values (mean +/- SEM) before and after treatment were assessed using analysis of variance. These data showed a significantly greater reduction of blood pressure with 4 mg and 8 mg daily doses compared to placebo and the 2 mg daily dose. Such results were not obtained with blood pressure levels recorded by a mercury sphygmomanometer, confirming the value of an automatic blood pressure recorder as a tool in therapeutic trials.