The relationship between the erythrocyte sedimentation rate (ESR), glycosylated hemoglobin, and the concentrations of plasma proteins was investigated in 34 outpatients with diabetes mellitus. Careful screening was performed to exclude infections. The ESR was found to be significantly elevated, the degree of elevation correlating with the serum globulin concentration, the albumin-globulin ratio, the serum fibrinogen concentration, and the percent glycosylated hemoglobin (HbA1c). Fasting serum glucose concentrations did not correlate with the ESR. The data indicate that the ESR in diabetic patient may be elevated in the absence of overt infection. The factors responsible for this elevation are discussed.