Xiaoke tea, a traditional Chinese treatment for diabetes mellitus, lowered blood glucose concentrations in streptozotocin diabetic mice. To investigate Xiaoke clinically, a double-blind crossover study was undertaken in 12 non-insulin-treated diabetic patients. Xiaoke tea and ordinary tea (infusion of 2.72 g, 4 times daily) were consumed in random order for 4 weeks. A standard breakfast meal was taken before and after each treatment period. Xiaoke did not significantly affect glycosylated haemoglobin, basal or post-breakfast serum glucose and insulin concentrations, intermediary metabolite concentrations, triglyceride and cholesterol. No adverse side-effects of Xiaoke were evident.