Vascular disease is the leading cause of death in patients with diabetes mellitus. Recent theories as to the pathogenesis of atherosclerosis have ascribed an important role to the platelet in the early stages of the disorder. Increased platelet aggregation in diabetes mellitus is considered to be one of the etiologic factors of diabetic microangiopathy. The aim of this investigation was to determine whether glucose and sorbitol change platelet aggregability on PRP. ADP induced platelet aggregation were evaluated in PRP, by densitometric assay in 40 healthy subjects after 30 minutes incubation with glucose(5-40mM), sorbitol(5-20mM). The results were as follows: 1. maximal platelet aggregation of PRP to ADP after 30 minutes incubation without glucose: 64.8%, with 10mM glucose: 62.5%, with 20mM glucose: 62.3%, with 40mM glucose: 60.6%. 2. maximal platelet aggregation of PRP to ADP after 30minutes incubation without sorbitol: 68.0%, with 5mM sorbitol: 70.0%, with 10mM sorbitol: 64.9%, with 20mM sorbitol: 64.3%. The platelet aggregation of PRP to 200microM ADP was not affected by glucose and sorbitol in this study. But other studies had shown that spontaneous platelet aggregation in samples of whole blood, but not in PRP, was found to be increased by glucose. This result suggest the involvement of RBC in the enhancement of spontaneous platelet aggregation in whole blood. In conclusion, the effect of glucose on platelet aggregation could be different due to different type of platelet preparation, and evaluation method of aggregation.