SummaryThis study reports a serologic method for the measurement of kidney-derived antigens in the urine of healthy children and of children with renal diseases. Two hundred twenty patients were studied. Four groups were recognized:group A, patients with no evidence of renal disease;group B, patients with past history of active urinary tract infection;group C, patients with active urinary tract infection;group D, patients with other renal diseases.Urinary renal antigen concentration was tested by the complement fixation method, in which titers of antigens in the urine were compared with a standard human renal antigen extract. The distribution of renal antigen concentrations ingroup Cdiffered significantly (P(X2) less than 0.001) from the other three groups. About 85% of patients ingroups A, B, andDhad levels below 0.6 mg/ml, whereas ingroup Conly 53% of patients had similar concentrations. After factoring the results by the urinary concentration of creatinine, 85% of patients ingroup Chad antigen levels above 0.6 mg/ml as opposed to 24%, 44%, and 27% ingroups A, B, andD, respectively. The results of the study are consistent with the assumption that the rate of discharge of renal antigenic material in the urine is accelerated in certain renal diseases.SpeculationTiters of renal antigen in urines of patients with urinary tract infection may differentiate parenchymal disease from lower tract disease. Monitoring of the pattern of renal antigen excretion may provide an index for optimal duration of antibacterial therapy in pyelonephritis.