The aim of this study was to compare the results of the 44-h ambulatory blood pressure monitoring (ABPM) data between haemodialysis (HDp) and CAPD patients and to investigate the relation of circadian rhythm in blood pressure (BP) with development of left ventricular hypertrophy. Twenty-two HDp (11 male, 11 female, mean age: 50 +/- 17 years) and 24 CAPDp (11 male, 13 female, mean age: 47 +/- 15 years) were included. Echocardiographic measurements and ABPM were performed in all study groups. ABPM of the first and second days were analysed separately and compared with CAPDp. Left ventricular hypertrophy was detected in 17 of the 22 HDp (77%) and 17 of the 24 CAPDp (71%). There was no significant differences between HD and CAPDp in respect to 44-h, daytime and night-time systolic and diastolic BP values. Although the course of BP in CAPDp was stable during the 44-h period, systolic and diastolic BP levels on the second day were significantly higher than those of on the first day in HDp (P < 0.001 for both). Daytime systolic and diastolic BP levels on the first day in HD group were recorded lower than those of the CAPD group. On the second day, night-time BP readings (both systolic and diastolic BP) were measured significantly higher in the HD group compared with the CAPD group. Twenty-one of the 24 (88%) CAPD patients were dippers, whereas only four of the 22 (18%) HDp were dippers (P < 0.001). Dipper patients had significantly lower left ventricular mass index (LVMI) than non-dipper patients (131 +/- 29 g/m(2) vs 153 +/- 40 g/m(2), P = 0.03). In 44-h ABPM, there were no differences in daytime and night-time systolic and diastolic blood pressures between HD and CAPD patients. Non-dipper patients had increased LVMI as compared with dipper patients. Abnormalities in circadian rhythm of the blood pressure might be one of the implicated factors for development of left ventricular hypertrophy.