We designed this study to examine whether uncontrolled hyperglycemia, duration of diabetes, or race (black v white) have any effect on glutathione levels in erythrocytes of type I diabetic patients. Hyperglycemia was assessed by measuring the level of hemoglobin A1c (HbA1c). Results show that erythrocytes of diabetic patients have a significantly lower glutathione level compared with those of age-matched normal subjects (P < .004). We found a significant negative correlation (r = -.59, P < .001) between the degree of hyperglycemia and the level of reduced glutathione (GSH) in erythrocytes of diabetic patients. There was no significant relationship (r = -.29, P > .12) between the level of GSH in erythrocytes and the duration of diabetes. Erythrocytes of black diabetic patients had significantly lower levels of GSH (P < .05) than those of white diabetic patients. Using erythrocytes as a model, this study suggests that a lower level of GSH may have a role in the cellular damage and impaired insulin secretion in uncontrolled diabetic patients.