Nonenzymatic glucosylation interferes with recognition of low density lipoprotein (LDL) by its receptor and markedly decreases the rate of plasma clearance of glucosylated LDL, both in experimental animals and in normal human subjects. However, in selected diabetic subjects we have observed a paradoxical increase in the clearance of glucosylated LDL, suggesting the possibility of immune-mediated clearance. Immunoassay demonstrated antibodies specific for glucosylated LDL in the preinjection plasma of each of four such diabetic subjects studied. These antibodies cross-react with other glucosylated proteins and recognize specifically the glucosylated lysine epitope--i.e., glucitollysine . These data suggest that nonenzymatic glucosylation of plasma or structural proteins may render them immunogenic and result in production of autoantibodies that recognize not only the particular immunogen but also many other glucosylated proteins, including glucosylated tissue proteins. These findings may be relevant to the increased prevalence of immune complexes in plasma of diabetic subjects and the late complications of diabetes mellitus.