Vesicoureteral reflux was defined as unilateral in 17 of 36 cases. Urine was collected from both kidneys. Urine specific gravity and osmolality were significantly reduced; beta 2-microglobulin was elevated and lactoferrin depressed on the reflux side. We also observed a significant correlation between specific gravity or osmolality on one side and lactoferrin on the other side, and between osmolality and beta 2-microglobulin. These observations showed a depressed concentrating capacity and reduced tubular absorption of beta 2-microglobulin suggesting reduced tubular function on the reflux side.