Non-enzymatic glycosylation of vascular wall collagen is considered to be most important in the pathogenesis of diabetic microangiopathy, and glycosylated collagens are reported to bind immunoglobulins in vivo. We investigated the occurrence of IgG or IgM deposits in the microvasculature of certain organs of diabetics using routine autopsy materials. Glomerular capillary basement membrane/endothelium was often positive for IgM in diabetics. Endothelial cells of glomerular capillaries were positive for HLA-DR in 6 of 16 diabetics and in 2 of 11 controls. This was associated with IgM or IgG deposits in 5 cases. In the esophagus and/or tongue of diabetics, IgG was frequently deposited in the microvasculature. In total, IgG deposits were found in 13 of 16 diabetics, either in the esophagus or the tongue, but in only 3 of 16 controls. The difference was significant at p less than 0.005. These observations suggest that deposition of immunoglobulins is a component of diabetic microangiopathy. Differences in expression of HLA-DR in glomeruli between diabetics and non-diabetics remain to be explored.