Leptin, the product of the ob gene, is a small peptide molecule synthesized by white adipocytes with an important role in the regulation of body fat and food intake. Based on the evidence that synthesis of leptin is regulated by female sex hormone, estrogen, this present study was investigated whether sex hormone precursor DHEA, can regulate obese gene expression in lean and genetically obese (ob/ob) mice. Antiobesity activity of DHEA was evaluated by determining body weight, food consumption, epididymal fat weight and serum levels of cholesterol and triglyceride in ICR, C57BL/6J, and ob/ob mice. The treatment of C57BL/6J lean and obese mice with a diet containing 0.3% and 0.6% DHEA resulted in lowered rates of weight gain in comparison to non-treated mice, although much greater response was found in the obese mice. All other concentrations of DHEA (0.015%, 0.06%, 0.15%, 0.3%) except the highest one(0.6%) showed no significant effects on weight gain in ICR mice. Food consumption was significantly decreased in all mice treated with 0.6% DHEA, whereas it was not decreased in ICR mice at lower concentrations than 0.6% DHEA. DHEA decreased significantly epididymal adipose tissue weight and serum triglyceride levels dose dependently in lean and obese mice. However serum cholesterol levels were decreased at lower concentrations than 0.15% DHEA and increased at concentrations of 0.3% and 0.6% DHEA in lean and obese mice. These increases in serum cholestrol levels at high concentrations of DHEA might result from the fact that DHEA has a cholesterol moiety thereby interfered the assay system. As an approach to elucidate the mechanism for antiobesity activity of DHEA, we examined mRNA levels of obese gene in the adipocyte and obese gene product (leptin) in the serum. The results showed that DHEA did not affect obese gene expression in ICR and C57BL/6J mice. Therefore, we concluded that antiobesity activity of DHEA was not modulated by obese gene expression.