In this double blind randomized study, blood pressure lowering effects and duration of action of two angiotensin converting enzyme (ACE) inhibitors were compared using home self blood pressure measurement (SBPM). After a two-week placebo run-in period, 128 hypertensive patients received during four weeks a daily morning dose of either perindopril (P) 4 mg or trandoplapril (T) 2 mg. One week of SBPM was planned at the end of both the run-in and the treatment period. Three consecutive measurements, with printed results, were requested in the morning before drug intake and in the evening. Run-in period home systolic (SBP) and diastolic (DBP) blood pressures were comparable in both groups: 149.9 +/- 14.5/97.3 +/- 8.1 mmHg in the P group (n = 63), 148.9 +/- 14.3/96.7 +/- 6.9 mmHg in the T group (n = 65). During the treatment period, evening BP was similar in the 2 groups: 139.1 +/- 14.3/89.9 +/- 9.1 mmHg in P group, 137.5 +/- 15.3/89.4 +/- 9.1 mmHg in T group (NS). On the other hand, morning BP was higher in the P group: 143.1 +/- 16.3/93.8 +/- 9.6 mmHg vs 137.4 +/- 16.7/90.3 +/- 9.7 mmHg (p < 0.05 for SBP and DBP-Student's t test). These results were confirmed by co-variance analysis after adjustment on initial BP. Due to standardized conditions of measurement, home SBPM was able to show a difference in BP lowering effects at the end of the inter-dose interval between two ACE inhibitors.