Microalbuminuria may be due to increased glomerular capillary pressure. In turn, this increased pressure may be associated to augmented protein intake or reduction of renal mass. 85 normal subjects who had a unilateral nephrectomy were studied. Creatinine clearance, microalbuminuria and blood pressure were measured. Hyperfiltration was evaluated by comparison of creatinine clearance before and after nephrectomy. Protein intake was evaluated by a nutritional questionnaire. Hyperfiltration was estimated as 38% and microalbuminuria was not different in patients submitted to nephrectomy (9.8 micrograms/min) compared to controls (9.7). Microalbuminuria post nephrectomy was not correlated to level of hyperfiltration, protein intake, age, blood pressure or time after surgery. These results suggest that the remaining kidney is able to double the excretion of albumin with a likely increase in glomerular filtration and intracapillary pressure.