The Chinese herbal medicine, Goshajinki- gan (GJ) (Niu-Che-Sen-Qi-Wan), has been widely used for treating patients with melalgia, lower back pain, numbness, and diabetic neuropathy. We investigated the effects of GJ on the regulation of serum insulin and triglyceride levels in obese Zucker fatty rats (fa/fa; ZFR). We administrated GJ to 6-week-old ZFR and non-obese lean rats (LR) for 12 weeks. Body weight and serum glucose, insulin, total cholesterol, and triglyceride levels were significantly increased at 18 weeks in ZFR as compared to the LR. GJ treatment in ZFR significantly suppressed elevation in serum glucose, insulin, and triglyceride levels, but no significant differences were observed in body weight and serum cholesterol levels in the ZFR group with GJ treatment compared to the ZFR group without GJ treatment. These results suggest that GJ may improve hyperinsulinemia and hypertriglyceridemia in ZFR and that GJ may be useful for preventing or delaying the onset of diabetes mellitus in a pre-diabetic state. [ABSTRACT FROM AUTHOR]