The aim of this study was to evaluate the influence of blood pressure variability and circadian rhythm on left ventricular mass and urinary albumin excretion rate (UAE) in patients with essential hypertension. 82 untreated patients (35 women and 47 men; mean age 41.1 +/- 13.7) were recruited to this study. Mean office blood pressure at entry was 152/97 mmHg. Ambulatory blood pressure monitoring (ABPM) was performed using an Medilog ABP recorder (Oxford). Blood pressure variability was estimated as the standard deviation (SD) of systolic and diastolic ambulatory blood pressure. Urinary albumin excretion (UAE) was estimated by the radioimmunoassay during two separate days. Echocardiography was used to measure left ventricular mass and left ventricular mass index (LVMI). The median urinary albumin excretion for the whole group was 8.2 mg/day; in 18 patients (21.9%) microalbuminuria was present. Left ventricular mass index in a whole group was 109.1 g/m2; in 23 subjects (28.0%) left ventricular hypertrophy (LVH) was found. Patients with microalbuminuria as well as with left ventricular hypertrophy had higher office and 24 hour ambulatory systolic and diastolic blood pressure and higher systolic blood pressure variability. During ABPM 18 patients with absent nocturnal fall in blood pressure (non-dippers) were found; they did not display more frequent prevalence of target organ damage. Increased 24-hour blood pressure variability present in hypertensive subjects with both microalbuminuria and left ventricular hypertrophy may suggest that this phenomenon plays role in development of target organ damage.