Abstract Some studies have recently reported increased production of platelet thromboxane and decreased vascular prostacyclin in patients with diabetes mellitus. The impact of these changes on platelet and vascular functions in vivo is still speculative. Using radio-immunoassay and high pressure liquid chromatography we have studied the plasma levels of 6-keto-PGF 1α, TXB 2 and PGE 2 in 23 juvenile-onset diabetics. There was Rio significant difference in these plasma prostaglandins between the diabetics and a control group. The prostaglandins were neither correlated to blood-glucose nor the degree of glycosylation (HbA 'Our results can not support the hypothesis that decreased vascular prostacyclin and increased platelet production of TXB 2 are important factors in diabetic patients.