Among 116 schoolgirls with asymptomatic bacteriuria detected at urinary screening, renal parenchymal reduction was found in 10.3%, while reflux was found in 20.7%. Only 30% of the 116 patients had a history referable to earlier urinary tract infection and there were remarkably few girls with an increased sedimentation rate (4.4%), C-reactive protein (9.5%), pyuria (25.8%) or lowered concentrating capacity (3.4%) at the time of detection of their bacteriuria. No method was found efficient in predicting lesions on the pyelogram and urethrocystogram, but determination of renal concentrating capacity and C-reactive protein was of some value in predicting parenchymal reduction. The girls with pyelonephritic changes on the pyelogram had a mean renal concentrating capacity significantly lower than the girls without changes. The concentrating capacity of the girls with reflux but without renal scarring and those bacteriuric patients without radiologically demonstrated defects did not differ significantly from the age-related normal values.