Microproteinuria was assessed by the measurement of albumin, retinol binding protein (RBP) and creatinine concentrations in random midstream urine samples using a single enzyme linked immunoassay (ELISA) in 36 children with vesicoureteric reflux (VUR) and 36 control patients. Infection was excluded by culture and microscopy of the specimens of urine. No patient was hypertensive. Albumin excretion increased in patients with increasing severity of VUR and with renal scarring. Similar findings were observed with RBP excretion. The results show that glomerular and tubular handling of proteins is altered in VUR. The degree of microproteinuria correlates well with the severity of the VUR and is evidence of tubular dysfunction. The effects of medical management and anti-reflux surgery on microproteinuria require further evaluation.