The value of glycosylated serum protein and glycosylated hemoglobin levels for estimating diabetic control was compared in 14 patients over 8 weeks during which glycemic control was improved. Glycosylated hemoglobin levels were not an effective indicator of improved glycemic control for the preceding 2 weeks; glycosylated serum protein values, however, accurately reflected alteration of mean glycemic levels 1 and 2 weeks after improvement of glycemic control. Both measurements were equally satisfactory after 8 weeks. In five patients glycosylated serum protein and glycosylated albumin values appeared equally effective in predicting glycemic control.