An increased thickness of the carotid artery wall is thought to be a sign of early atherosclerosis. Since plasma endothelin concentrations were released from vascular endothelial cells, we have investigated the possible relationship between endothelin 1 (ET-1) and arterial wall thickness. Ninety-eight patients with Type 2 diabetes without evidence of macroangiopathy, hypertension, proteinuria or proliferative retinopathy, and 50 non-diabetic subjects were studied. After an overnight fast, blood was taken for ET-1, glucose, HbA1c, lipids, insulin and C-peptide. Arterial wall thickness was measured as the mean of the maximum intimal-medial thickness (IMT) in 16 carotid segments by B-mode ultrasound. ET-1 levels were significantly elevated in diabetic patients with IMT>1100 microm, 8.3 pmol/l (5.2-12.9) compared with control subjects, 7.6 pmol/l (5.0-11.0), p<0.01 and with diabetic subjects with IMT<500 microm, 7.43 pmol/l (4.8-11.1), p<0.01. The diabetic (IMT>1100 microm) study group had also significantly higher levels of insulin, 102.8 +/- 46.4 pmol/l vs control subjects, 77.5 +/- 32.4 pmol/l, p<0.01. In diabetic subjects, no correlation was found between ET-1 and IMT with glucose, HbA1c, lipids, age or duration of diabetes, respectively. We conclude that ET-1 levels are elevated in Type 2 diabetic patients with increased IMT. Thus providing further support for the role of endothelin in atherosclerosis.