Abstract: β₂-microglobulin （β₂m） is continuously produced and subsequently almost exclusive- ly eliminated by the kidneys.Its level in serum,therefore,may reflect the renal func- tion status.In the present report,serum β₂m concentrations were measured by RIA in 77 cases of diabetes millitus,including 15 cases with diabetic nephropathy and 22 cas- es with simple diabetic retinopathy.Serum creatinine and blood urea nitrogen were det- ermined simultaneously for comparison.Serum β₂m concentrations were found to be hig- hest in patients with diabetic nephropathy,and were higher in patients with diabetic re- tinopathy than in those without detectable microvascular diseases.For the detection of renal function impairment,serum β₂m correlated well with serum creatinine and blood urea nitrogen,and gave the highest positive rate among the three tests.The results of this study suggest that measurement of serum β₂m might be a sensitive method in dete- cting early and minor impairment of renal function in diabetics.