To evaluate the secretion of vasoactive factors in vascular endothelium of patients with non-insulin-dependent diabetes mellitus (NIDDM) the authors examined 31 NIDDM patients. Of them, 18 had no signs of renal involvement, 13 patients showed apparent diabetic nephropathy (DN). In the former patients the blood contained much greater content of vasodilating factor prostacyclin than of vasoconstricting factor endothelin-1 (ET-1) and thromboxan A2 (TxA2). In diabetic nephropathy the balance of vasoactive factors shifted to predominance of vasoconstrictors ET-1 and TxA2. Such rearrangement of vasoactive factors to higher quantities of vasoconstrictors in diabetes mellitus may initiate or promote progression of diabetic nephropathy with resultant spasm of afferent glomerular vessels, reduced glomerular filtration and renal blood flow rates, arterial hypertension, increased thrombogenesis. Thus, elevated levels of ET-1 and TxA2 in diabetics and their rise with progression of diabetic nephropathy are likely to act as pathogenetic factors underlying onset and progression of nephroangiopathy.