The present study aimed to evaluate the temporal course and the pattern of urinary protein excretion in SHR. Urinary protein excretion was evaluated in both 5, 14 and 21 week-old SHR and WKY rats. Daily urinary protein excretion increased with age in SHR, but remained unchanged in WKY rats. At 5 weeks of age, when SHRs were still in the pre-hypertesive stage, no differences were observed on daily urinary protein excretion between SHR and age-matched WKY. However, SHRs displayed higher urinary protein excretion compared to the WKY at 14 (80 ± 4 vs. 34 ± 7 mg/kg/day) and 21 weeks of age (130 ± 6 vs. 39 ± 7 mg/kg/day). SDS-PAGE analysis of urinary proteins showed that both SHR and WKY rats only excreted proteins of the size of albumin or smaller. Additionaly, SHR presented a progressive increase of intact urinary albumin excretion from 5 to 21-weeks of age. Rate of progression of microalbuminuria correlated with elevation of arterial blood pressure in SHR (0.68; P<0.01). Consistent with these findings, the expression of the endocytic receptor megalin decreased with age in SHR. Changes on megalin expression were not observed in WKY rats. Taken together, these data suggest that SHR displays tubular proteinuria after devolpment of hypertension at least in part due to a decrease of megalin expression in renal proximal tubule.