This randomised, double-blind, double-dummy, parallel group, multicentre study compared the efficacy and tolerability of lercanidipine with lacidipine. Elderly patients with isolated systolic hypertension (supine blood pressure >/=160/<95 mmHg) were enrolled and underwent a placebo run-in period of 14-27 days before random allocation to lercanidipine tablets 10 mg once daily (n=111) or lacidipine tablets 2 mg once daily (n=111) for the assessment period (112-160 days). Titration to lercanidipine 20 mg once daily (two 10 mg tablets) or lacidipine 4 mg once daily (two 2 mg tablets) was allowed after 8 weeks, if required. Both treatments decreased supine and standing systolic and diastolic blood pressure between the end of the run-in period and the end of the assessment period (P<0.0001). At the end of the assessment period, the estimated mean treatment difference (95% confidence intervals) in supine systolic blood pressure was -0.81 (-4.45, 2.84) mmHg. These confidence intervals were within the limits specified for equivalence, that is, (-5, 5) mmHg. Ambulatory blood pressure monitoring showed that the antihypertensive effects of both drugs lasted for the full 24-h dosing period and followed a circadian pattern. Both treatments were well tolerated with a low incidence of adverse drug reactions and a low withdrawal rate. Significantly fewer patients withdrew from treatment with lercanidipine (P=0.015). Neither treatment had any clinically significant effect on pulse rate or cardiac conduction. In conclusion, both treatments were equally effective in controlling supine systolic blood pressure in patients with isolated systolic hypertension.