This study aims to evaluate the clinical and biochemical profile associated with the presence of microalbuminuria in a group of essential hypertensive patients referred to a hypertension clinic. A total of 188 non-diabetic, untreated essential hypertensive patients (100 men, 88 women) aged 55.8 +/- 11.7 years are studied. Urinary albumin excretion was determined in two 24-h urine collections. Clinical and biochemical evaluations and 24-h ambulatory blood pressure (BP) monitoring were performed at baseline. Forty-two patients (22.3%) showed an increased urinary albumin excretion rate (20-200 micrograms/min). These patients showed significantly higher values (P < 0.01) for 24-h, daytime and night-time systolic and diastolic BP, compared with essential hypertensives with normal urinary albumin excretion. However, nocturnal reduction in BP did not differ between the groups. Furthermore, patients with microalbuminuria showed significantly higher (P < 0.01) creatinine, serum uric acid and triglycerides, as well as lower high-density lipoprotein (HDL)-cholesterol. In a multiple logistic regression analysis, a 24-h systolic BP > 140 mmHg (odds ratio: 3.19; 95% confidence interval [CI 95%]: 1.44-7.06) and a serum creatinine > 88 mumol/L (odds ratio: 3.08; CI 95%: 1.39-6.84) were the two factors associated independently with increased urinary albumin excretion. We conclude that, in essential hypertensive patients, the presence of microalbuminuria is associated with elevated BP, but not with its circadian pattern. Likewise, microalbuminuria is associated with the degree of renal impairment, and with increased uric acid and triglycerides and decreased HDL-cholesterol.