We investigated the effects of garlic oil and diallyl trisulfide on glycemic control in rats with streptozotocin-induced diabetes. Diabetic rats received by gavage garlic oil (100 mg/kg body weight), diallyl trisulfide (40 mg/kg body weight), or corn oil every other day for 3 weeks. Control rats received corn oil only. Both garlic compounds significantly raised the basal insulin concentration. The insulin resistance index as assessed by homeostasis model assessment and the first-order rate constant for glucose disappearance were significantly improved by both garlic compounds (P<0.05). Oral glucose tolerance was also improved by both garlic compounds and was accompanied by a significantly increased rate of insulin secretion (P<0.05). Glycogen formation (but not that of lactate or carbon dioxide) from glucose by the soleus muscle in the presence of 10 or 100 microU/ml of insulin was significantly better after treatment with both garlic compounds. Both garlic oil and diallyl trisulfide improve glycemic control in diabetic rats through increased insulin secretion and increased insulin sensitivity.