Renal function studies were done on asymptomatic hyperuricemic subjects and normouricemic controls matched as to age, sex and blood pressure. Abnormal urinary sediments and proteinuria were found more frequently in asymptomatic hyperuricemic subjects than in the controls. In addition, the maximal osmolar concentrating ability of urine was markedly reduced in the asymptomatic hyperuricemic subjects. There was no difference in renal function measured by Phenolsulfonphthalein excretion between the groups. Our results suggest that hyperuricemia alone may contribute to renal tubular impairment.