Recently, nicotinic acid has been recommended as a first-line hypolipidemic drug. To determine the effectiveness of nicotinic acid in dyslipidemic patients with non—insulin-dependent diabetes mellitus, 13 patients were treated in a randomized crossover trial. Patients received either nicotinic acid (1.5 g three times daily) or no therapy (control period) for 8 weeks each. Compared with the control period, nicotinic acid therapy reduced the plasma total cholesterol level by 24%, plasma triglyceride level by 45%, very-low-density lipoprotein cholesterol level by 58%, and low-density lipoprotein cholesterol level by 15% and it increased the high-density lipoprotein cholesterol level by 34%. However, nicotinic acid therapy resulted in the deterioration of glycemic control, as evidenced by a 16% increase in mean plasma glucose concentrations, a 21% increase in glycosylated hemoglobin levels, and the induction of marked glycosuria in some patients. Furthermore, a consistent increase in plasma uric acid levels was observed. Therefore, despite improvement in lipid and lipoprotein concentrations, because of worsening hyperglycemia and the development of hyperuricemia, nicotinic acid must be used with caution in patients with non—insulin-dependent diabetes mellitus with dyslipidemia. We suggest that the drug not be used as a first-line hypolipidemic drug in patients with non—insulin-dependent diabetes mellitus.