The anionic charge on the surface of the erythrocyte and the erythrocyte membrane content of sialic acid and acid glycosaminoglycans (GAGs) were evaluated in insulin-dependent diabetic patients who had albumin excretion rates less than 300 mg/24 h. In these subjects a statistically significant reduction of erythrocyte anionic charge (RBCCh) and GAGs content in erythrocyte ghosts was shown. In view of the demonstration of a negative correlation between RBCCh and albuminuria after a lysine provocative test, these observations support the hypothesis that the onset of microalbuminuria in human diabetes is sustained by an alteration of glomerular charge and consequently of glomerular charge selectivity.