We evaluated renal functional reserve (RFR) in 36 patients aged 5-21 years, who had recovered from an acute episode of poststreptococcal glomerulonephritis (PSGN) 1-16 years previously, without apparent sequelae, as evidenced by normal serum creatinine, blood pressure, and urinary sediment. The control group consisted of 12 children aged 2-12 years with recurrent urinary tract infections or nocturnal enuresis, without active infection or anatomical anomalies. The basal creatinine clearance was similar in the PSGN and control groups: 140.0 +/- 27.4 ml/ min per 1.73 m2 and 142.9 +/- 15.5 ml/min per 1.73 m2, respectively. The RFR in the PSGN group was significantly reduced compared with that of the control group: 18.6 +/- 12.9 ml/min per 1.73 m2 and 41.1 +/- 25.3 ml/min per 1.73 m2, respectively (P < 0.02). In 7 PSGN patients (19.4%), no RFR was found. In 69% of patients who had recovered from PSGN more than 10 years before the protein loading tests, a significantly reduced RFR (less than 10% of baseline) was found. The same degree of reduction in RFR was found in only 26% of patients who had suffered from PSGN less than 10 years ago.