This multicenter, randomized, placebo-controlled study of glimepiride, a new oral sulfonylurea, was conducted in patients with type 2 diabetes for whom dietary treatment was unsuccessful (fasting plasma glucose [FPG] = 151-300 mg/dL) during a 1-week screening period. Patients were randomized to receive glimepiride (n = 123) or placebo (n = 126) once daily for a 10-week dose-titration period, then maintained on an individually determined optimal dose (1-8 mg of glimepiride or placebo) for 12 weeks. Glimepiride lowered FPG by 46 mg/dL, hemoglobin A1C (HbA1C) by 1.4%, and 2-hour postprandial glucose by 72 mg/dL more than placebo. Glimepiride improved postprandial insulin and C-peptide responses without producing clinically meaningful increases in fasting insulin or C-peptide levels. Good glycemic control (HbA1C < or = 7.2%) was achieved by 69% of the patients taking glimepiride versus 32% of those taking placebo. The overall incidence of adverse events was similar in both groups. No clinically noteworthy abnormal laboratory values or hypoglycemia (blood glucose < 60 mg/dL) occurred. Glimepiride is safe and effective for treatment of patients with type 2 diabetes for whom diet therapy is unsuccessful.