The natural compounds genistein (G), quercetin (Q), and resveratrol (R) have been reported to each exhibit anti-adipogenic activities in adipocytes and antiproliferative and pro-apoptotic activities in several cell types. We studied the combined effects of G, Q, and R on adipogenesis and apoptosis in primary human adipocytes (HAs) and 3T3-L1 murine adipocyte (MAs). Combined treatment with 6.25 microM G, 12.5 microM Q, and 12.5 microM R during the 14-day differentiation period caused an enhanced inhibition of lipid accumulation in maturing HAs that was greater than the responses to individual compounds and to the calculated additive response. Glycerol 3-phosphate dehydrogenase activity, a marker of late adipocyte differentiation, was decreased markedly in HAs treated with the combination of G+Q+R. In addition, combined treatment with 50 microM G, 100 microM Q, and 100 microM R for 3 days decreased cell viability and induced apoptosis in early- and mid- phase maturing and lipid-filled mature HAs. In contrast, no compound alone induced apoptosis. Oil Red O stain and Hoechst 33342 stain were performed to confirm the effects on lipid accumulation and apoptosis, respectively. We also determined whether MAs responded to the combination treatment similarly to HAs. As in HAs, G+Q+R treatment decreased lipid accumulation in maturing MAs and increased apoptosis in pre- and lipid-filled mature MAs more than the responses to G, Q, and R when used separately. These results show that lower concentrations of combined treatments with several natural compounds may be useful for treatments for obesity through the suppression of adipogenesis and enhanced adipocyte apoptosis.