Although nephrotic-range proteinuria and progressive azotemia are unequivocal indications of disordered glomerular function in patients with long-standing insulin-dependent diabetes mellitus, it is apparent that alterations in glomerular function also occur at an early stage of this disease in humans and experimental animals. Stalder and Schmid1 reported more than 20 years ago that the glomerular filtration rate (GFR) is elevated above normal in diabetic children and young adults, a finding confirmed by Ditzel and Schwartz2 and extensively investigated in recent years by Mogensen.3,4 Mogensen described a 40% increment in GFR in 11 newly diagnosed juvenile diabetic patients when compared with values in 31 normal subjects of similar age.3 This remarkable hyperfiltration was shown to be related to the patient’s metabolic status since reduction of blood sugar levels over several days to weeks by standard insulin therapy tended to return GFR to normal or near-normal levels. Indeed, recent studies by Christiansen et al.5 have demonstrated that with reduction in blood glucose levels to normal in diabetics by continuous insulin infusion, GFR also declines from elevated to near-normal values in a matter of hours.