The aim of this study was to determine the relationship between urinary albumin excretion (UAE), cardiac structural changes upon echocardiography and 24-h ambulatory blood pressure (ABPM) levels. Twenty mild hypertensive patients (mean age 56.8 +/- 9.6 years) were evaluated. After 2 weeks of a washout period of all antihypertensive drugs, all patients underwent an echocardiographic evaluation, a 24-h ABPM and an overnight urine collection. Systolic and diastolic blood pressure during 24-h ABPM was 145 +/- 14/91 +/- 10 mmHg (daytime) and 130 +/- 14/76 +/- 8 mmHg (nighttime), respectively. Seven (35%) patients presented UAE > or = 15 microg/min, and for the whole group, the geometric mean value for UAE was 10.2 x// 3.86 microg/min. Cardiac measurements showed mean values of interventricular septum thickness (IVS) of 11 +/- 2.3 mm, left ventricular posterior wall thickness (PWT) of 10 +/- 2.0 mm, left ventricular mass (LVM) of 165 +/- 52 g, and left ventricular mass index (LVMI) of 99 +/- 31 g/m2. A forward stepwise regression model indicated that blood pressure levels did not influence UAE. Significant correlations were observed between UAE and cardiac structural parameters such as IVS (r = 0.71, P<0.001), PWT (r = 0.64, P<0.005), LVM (r = 0.65, P<0.005) and LVMI (r = 0.57, P<0.01). Compared with normoalbuminuric patients, those who had microalbuminuria presented higher values of all cardiac parameters measured. The predictive positive and negative values of UAE > or = 15 microg/min for the presence of geometric cardiac abnormalities were 75 and 91.6%. These data indicate that microalbuminuria in essential hypertension represents an early marker of cardiac structural damage.