Elevated levels of hepatic enzymes, hepatocellular inflammation, and viral susceptibility are known to occur with increased frequency in individuals with type 2 diabetes mellitus regardless of the type of antidiabetic therapy used. Subject to the approval of pioglitazone, the Food and Drug Administration requested a 3-year outcome study evaluating the occurrence of serious liver disease in subjects treated with pioglitazone. The present study was designed to fulfill this phase 4, postmarketing commitment to the Food and Drug Administration, pursuant to demonstrating the long-term hepatic safety of pioglitazone. This study was designed to determine whether pioglitazone is associated with a difference in the incidence of elevated levels of alanine aminotransferase, a marker of hepatocellular inflammation or injury, when compared with glyburide. Glyburide is used for treatment of patients with type 2 diabetes mellitus; its use in this study as a comparator should provide a basis for evaluating whether pioglitazone is associated with an increased risk of hepatocellular inflammation or injury.