Aim: To evaluate the efficacy and safety of alogliptin, a potent and highly selective dipeptidyl peptidase-4 (DPP-4) inhibitor, in combination with glyburide in patients with type 2 diabetes inadequately controlled by sulphonylurea monotherapy. Methods: After a 2-week screening period, adult patients 18-80 years of age entered a 4-week run-in/stabilization period in which they were switched from their own sulphonylurea medication to an equivalent dose of glyburide (open label) plus placebo (single blind). After the run-in period, patients were randomly assigned to double-blind treatment with alogliptin 12.5 mg (n = 203), alogliptin 25 mg (n = 198), or placebo (n = 99) for 26 weeks. The primary end-point was change from baseline to week 26 in glycosylated haemoglobin (HbA1c). Secondary end-points included clinical response rates and changes in fasting plasma glucose, β-cell function (fasting proinsulin, insulin, proinsulin/insulin ratio, and C-peptide, and homeostasis model assessment β-cell function), body weight, and safety end-points [adverse events (AEs), clinical laboratory tests, vital signs and electrocardiographic readings]. Results: The study population had a mean age of 57 years and a mean disease duration of 8 years; it was well balanced for gender (52% women) and was mainly white (71%). The mean baseline HbA1c was approximately 8.1% in each group. Significantly greater least squares (LS) mean reductions in HbA1c were seen at week 26 with alogliptin 12.5 mg (-0.38%) and 25 mg (-0.52%) vs. placebo (+0.01%; p < 0.001), and more patients in the alogliptin 25-mg group had HbA1c levels ≤7.0% at week 26 (34.8%, p = 0.002) vs. placebo (18.2%). Proportionately more patients in the alogliptin 12.5 mg (47.3%) and 25 mg (50.5%) groups had an HbA1c reduction ≥0.5% from baseline compared with patients in the placebo group (26.3%; p < 0.001). Minor improvements in individual markers of β-cell function were seen with alogliptin, but no significant treatment group differences were noted relative to placebo. Minor LS mean changes in body weight were noted across groups (placebo, -0.20 kg; alogliptin 12.5 mg, +0.60 kg; alogliptin 25 mg, +0.68 kg). AEs were reported for 63-64% of patients receiving alogliptin and 54% of patients receiving placebo. Few AEs were treatment limiting (2.0-2.5% across groups), and serious AEs (2.0-5.6%) were infrequent, similar across groups, and generally considered not related to treatment. The incidences of hypoglycaemia for placebo, alogliptin 12.5mg and alogliptin 25 mg groups were 11.1, 15.8 and 9.6% respectively. Conclusions: In patients with type 2 diabetes inadequately controlled by glyburide monotherapy, the addition of alogliptin resulted in clinically significant reductions in HbA1c without increased incidence of hypoglycaemia. © Journal Compilation © 2008 Blackwell Publishing Ltd.