The purpose of the present study was to examine the effects of salt-restriction alone and in combination with an angiotensin-converting enzyme (ACE) inhibitor (cilazapril) on both office and ambulatory blood pressure (BP) levels in free living subjects with elevated BP. The study was carried out in an out-patient setting with subjects recruited from occupational health care system mainly. After exclusions, 39 subjects (24 men, 15 women, aged 28-65 years) with mildly to moderately elevated BP completed the study. After 3 months run-in period with placebo (first month on normal-salt and the next 2 months on sodium-restricted diet) the subjects were randomised into either salt-restriction placebo or salt-restriction cilazapril (2.5 mg daily) groups for 3 months. In the whole group, 24-h urinary sodium excretion decreased (mean +/- s.d.) from 198 +/- 60 to 112 +/- 59 mmol (4 weeks vs 24 weeks, P < 0.001). Systolic and diastolic office BP decreased during the placebo-sodium-restriction phase (-7.1 [95% Cl -11.2; -3.0] and -4.2 [95% Cl -6.6; -1.8] mm Hg for systolic and diastolic BP), and similarly the daytime ambulatory BP (ABP) was reduced during this period (-2.8 [95% Cl -5.2; -0.5] and -2.8 [95% Cl -4.5; -1.2] mm Hg, systolic (SBP) and diastolic blood pressure (DBP) respectively). No changes were observed in the night time ABP. Addition of cilazapril to sodium-restriction enhanced significantly the office BP (-13.2, [95% Cl -20.2; -6.2], and -9.1 [95% Cl -13.5; -4.7]) and daytime ABP (-5.9, [95% Cl -10.1; -1.8] and -5.3, [95% Cl -8.8; -1.9]) reduction. Blood glucose, plasma insulin or serum lipids did not change during the study. Moderate sodium restriction seems to lower the office and daytime ABP levels in subjects with mild-to-moderate hypertension. The antihypertensive effect of cilazapril could be enhanced by sodium restriction.