The aim of this work was to evaluate the prevalence of microalbuminuria in an obese population and to study the relation between albumin excretion rate (AER), various clinical (body mass index, adipose tissue distribution) nutritional (macronutrient intake) and metabolic parameters. A cross-sectional study was carried out, and AER was evaluated in 182 obese subjects (BMI > 27) with no medication, no intercurrent disease, no cardiac, pulmonary or endocrinological disorders (including diabetes and hypertension) and also in 31 control subjects at the outpatient clinic of the department of Nutrition, Hôtel Dieu, Paris, France. The following were measured: BMI, waist/hip ratio (WHR), urinary AER, blood glucose, insulin and C peptide levels, cholesterol (CT), triglycerides, HDL cholesterol (HDL-CT), apoprotein A1 and B. In the obese population, 18 subjects (9.9%) were found to have an increased AER: 13 subjects (7.1%) with microalbuminuria (AER between 30 to 300 mg/24 h) and five with AER over 300 mg/24 h. AER was normal in all control subjects but one, who was found to have microalbuminuria. Log AER was positively correlated to WHR (P < 0.001), blood pressure (P < 0.05), cholesterol (P < 0.05), Apo B levels (P < 0.01) and with fasting Insulin levels and protein intake (P < 0.001). Positive association between log AER and protein intake, insulin levels, Apo B and blood pressure were found independently of BMI and WHR. It is suggested that abdominal obesity may be associated with incipient nephropathy in some obese subjects without diabetes and hypertension. Microalbuminuria may be included among metabolic abnormalities connected with abdominal-type excess weight distribution.(ABSTRACT TRUNCATED AT 250 WORDS)