We studied serum thromboxane (TXB2), the prostacyclin metabolite, 6-keto-PGF1 (6KPGF1) glucose, insulin, and lipid/lipoprotein profiles in 27 patients with non-insulin-dependent diabetes mellitus (NIDDM) who were switched from therapy with glibenclamide (GLB) (with [GLBH] or without phenformin) to gliclazide for 3 months. We found that therapy with gliclazide was followed by a decrease in serum TXB2 (281.8 +/- 128.3 to 149.1 +/- 77.0 mg/L, P less than .001) and an increase in serum 6KPGF1 (60.5 +/- 19.1 to 96.0 +/- 40.3 mg/L, P less than .001). This was accompanied by a decrease in total and low-density lipoprotein (LDL) cholesterol and an increase in high-density lipoprotein (HDL) cholesterol, within the HDL3 cholesterol fraction. These changes were seen despite the fact that neither fasting plasma glucose nor insulin changed with therapy. These findings suggest that gliclazide may have beneficial actions on cardiovascular risk factors in these NIDDM patients.