In the present study, we examined the circadian profile of blood pressure (BP) in 10 patients with moderate essential hypertension before and after 6 months of lacidipine therapy. Ambulatory BP was measured at 30-min intervals using SpaceLabs 90207. To account for the unequal time intervals between successive readings, BP means and variances were weighted for the time span between successive readings, and weighted linear-regression analysis was applied. The 24-h BP values were carried out using Fourier analysis, comparing the values from the baseline with those after 24 weeks of lacidipine. After 24 weeks BP values showed a significant decrease compared with baseline values (all p < 0.01). The daily BP curves obtained from Fourier analysis with four harmonics showed that the significant circadian rhythm in nine patients was not altered by lacidipine treatment. The night/day differences were statistically significant at 24 weeks vs. 0 week (all p < 0.01). The overall amplitude and acrophase of the BP curve were statistically significant at 24 weeks (all p < 0.01). After 24 weeks of lacidipine therapy, according to the nocturnal BP fall, we found three intermediate dippers, six dippers, and one non-dipper. By use of the two-step Fourier analysis method, which provides a formal and statistical method to evaluate the presence of a significant diurnal BP rhythm and parametrization of the 24-h BP recordings, we showed that lacidipine long-term therapy is effective in lowering BP and preserving the diurnal BP rhythm.