The Precose Resolution of Optimal Titration to Enhance Current Therapies (PROTECT) trial was a nationwide postmarketing study designed to assess the effectiveness, tolerability, and safety of acarbose in patients with type 2 diabetes mellitus. This prospective, multicenter, open-label, 28-week trial enrolled 6142 patients who had type 2 diabetes that was inadequately controlled with either diet alone or diet plus a sulfonylurea. The dosage of acarbose was titrated from 25 mg TID to 50 mg TID (forced titration) and then titrated from 50 mg TID to 100 mg TID based on tolerability and efficacy. Efficacy of glycemic control was assessed by recording changes in glycated hemoglobin A1c (Hb A1c) and 1-hour postprandial plasma glucose (PPG) levels. Tolerability and safety were determined on the basis of patients' reports of treatment-emergent adverse events and by review of laboratory test results. Acarbose was safe and effective in improving glycemic control in patients with type 2 diabetes, regardless of their age, weight, ethnic background, time since diagnosis, or concomitant sulfonylurea therapy. Hb A1c levels declined throughout the treatment period, for a mean change in Hb A1c of -0.66%. The mean change from baseline in 1-hour PPG levels was -41 mg/dL at the end of treatment. Although all types of patients enrolled in the study responded positively to acarbose therapy, certain subgroups responded particularly well, especially those who had been diagnosed with the disease for less than 1 year and those who were untreated at study entry. Adverse events consisted primarily of gastrointestinal disturbances.