Erythrocyte Na+/Li+ countertransport activity was investigated in 11 controls and 22 recent onset type I (insulin-dependent) diabetic patients with normal and high glomerular filtration rates. No differences in Vmax were observed in hyperfiltering compared to normofiltering patients or controls. The Na+/Li+ activity was correlated with blood glucose levels in insulin-dependent diabetics showing good glycemic control. Total cholesterol and triglyceride concentrations were similar among the three groups. In conclusion, enhanced Na+/Li+ countertransport activity is not associated, in our case, with diabetic condition per se and with early glomerular hyperfiltration and cannot be used as a marker of renal involvement in recent onset insulin-dependent diabetics.