Apoptosis of preadipocytes and adipocytes contributes to the balance of adipose tissue mass by reducing adipocyte number. To address this phenomenon, we treated cultured rat S-V cells with all-trans-retinoic acid (RA) (10 mu M) or C2-ceramide (50 mu M) during adipogenesis. Gel electrophoresis of DNA from treated cells cultured in serum-free medium showed that 10 mu M Rei or 50 mu M ceramide induced a distinct laddering pattern of DNA fragments. Cellular caspase 3 activity, another marker of apoptosis, was increased by RA (10 mu M) (P < 0.05), but not by 50 mu m CB-ceramide. RT-PCR results showed that RA (10 mu M) decreased the expression of Bcl-2 mRNA These results suggest that fat cell loss by apoptosis can be regulated, in part, by RA (10 mu M) which increases caspase 3 activity and decreases Bcl-2 expression in rat S-V cells. CB ceramide apparently works through a different cellular mechanism to induce apoptosis.