Glycosylated hemoglobin (HbA1) is widely used as an index of glycemic control in diabetic patients. However, due to the long survival time of erythrocytes (120 days), it remains elevated for several weeks after improved control. Other plasma proteins are similarly glycosylated, and as glycosylated serum albumin (GSA) has a shorter half-life (20 days), it should detect glycemic changes earlier. Fasting blood glucose (FBG), GSA, and HbA1 were measured weekly in newly diagnosed diabetic patients (N = 12) for 8 wk after beginning treatment. After 4 wk, a similar fall in FBG and GSA levels, i.e., 72% and 58% respectively, was observed. In contrast, HbA1 fell significantly less (P less than 0.01), by only 39% of its initial value. By 8 wk there was no significant difference between the percentage reduction in the three indices of control. Therefore, GSA provides the clinician with earlier objective evidence of the metabolic response to therapeutic intervention and can be regarded as an intermediate index of diabetic control.