This prospective, 1-year, multicenter, double-blind, randomized, parallel-group study was designed to show that repaglinide was at least equivalent to glyburide in patients with type 2 diabetes. Five hundred and seventy-six patients with type 2 diabetes of at least 6 months' duration were randomized to receive monotherapy with repaglinide (n = 383) or glyburide (n = 193). During weeks 1-8, doses were gradually increased to achieve a target fasting plasma glucose (FPG) range of 80-140 mg/dl. The final adjusted dose was maintained for 12 months. Repaglinide patients received a starting dose of 0.5 mg three times/day preprandially, adjusted as necessary to 1, 2 or 4 mg before breakfast, lunch and dinner. Glyburide patients received a starting dose of 2.5 mg before breakfast and placebo before lunch and dinner. Glyburide was increased as necessary to 5 or 10 mg before breakfast (placebo before lunch and dinner) or to 15 mg (10 mg before breakfast, placebo before lunch, and 5 mg before dinner). After study drug was stopped, patients were transferred to an appropriate therapy, as recommended by the investigator. Efficacy was assessed by changes from baseline in glycemic control parameters and in C-peptide, insulin, and lipid profiles. Repaglinide provided glycemic control that was at least as effective and potentially safer than that provided by glyburide. The glucose-lowering effect of repaglinide was most pronounced in pharmacotherapy-naive patients, who showed rapid and marked decreases in mean glycosylated hemoglobin levels from baseline (9.4%) to month 3 (7.6%) and month 12 (7.9%). Mean FPG levels also decreased overall in this group, from 222 mg/dl at baseline, to 175 mg/dl at month 3, to 188 mg/dl at month 12. At endpoint, morning C-peptide levels had increased significantly in glyburide-treated patients compared with those treated with repaglinide, but morning fasting insulin levels did not differ significantly between the two groups. Repaglinide efficacy was sustained over 1 year and was not influenced by age or sex. Overall safety and changes in lipid profile and body weight were similar with both agents, with no significant change after extended pharmacotherapy. Weight gain data for the subset of pharmacotherapy-naïve patients suggest that patients given repaglinide may gain less weight than those given glyburide. Repaglinide, at doses of 0.5-4.0 mg administered three times preprandially, was well tolerated and provided safe and consistently effectiveglycemic control during this 1-year study. Patients using repaglinide received the same therapeutic benefits as those using glyburide, and may have received additional benefits.