MLR-1023 [Tolimidone; CP-26154; 2(1H)-pyrimidinone, 5-(3-methylphenoxy)] is an allosteric Lyn kinase activator that reduces blood glucose levels in mice subjected to an oral glucose tolerance test (J Pharmacol Exp Ther 34215-22, 2012). The current studies were designed to define the role of insulin in MLR-1023-mediated blood glucose lowering, to evaluate it in animal models of type 2 diabetes, and to compare it to the activities of selected existing diabetes therapeutics. Results from these studies show that in an acute oral glucose tolerance test MLR-1023 evoked a dose-dependent blood glucose-lowering response that was equivalent in magnitude to that of metformin without eliciting a hypoglycemic response. In streptozotocin-treated, insulin-depleted mice, MLR-1023 administration did not affect blood glucose levels. However, MLR-1023 potentiated the glucose-lowering activity of exogenously administered insulin, showing that MLR-1023-mediated blood glucose lowering was insulin-dependent. In a hyperinsulinemic/euglycemic clamp study, orally administered MLR-1023 increased the glucose infusion rate required to sustain blood glucose levels, demonstrating that MLR-1023 increased insulin receptor sensitivity. In chronically treated db/db mice, MLR-1023 elicited a dose-dependent and durable glucose-lowering effect, reduction in HbA1c levels and preservation of pancreatic β-cells. The magnitude of effect was equivalent to that seen with rosiglitazone but with a faster onset of action and without causing weight gain. These studies show that MLR-1023 is an insulin receptor-potentiating agent that produces a rapid-onset and durable blood glucose-lowering activity in diabetic animals.