Materials and Methods Cell Culture, Differentiation, and TNF-a Treatment. 3T3-L1 preadipocytes were grown in 150-mm culture dishes in Dulbecco’s modified Eagle’s medium (DME)(Gibco) supplemented with 2 mM glutamine (Rubin et al., 1978) and 10% fetal calf serum(Gibco). Cultures were fed 18 mL of medium every 2-3 days during exponential growth and ac-cording to the schedule described below during differentiation (Smith et al., 1988). The cells were maintained in an atmosphere of 10% C02 and 90% air at 37 C. Preadipocytes that were grown to confluence in 150-mm culture dishes were subjected to the differentiation protocol (Rubin et al., 1978). Confluent cells were fed with 18 mL of fresh standard medium containing 0.5 mM l-methyl-3-isobutylxanthine and 0.5^ M dexamethasone. After 48 h, the medium containing the steroid and l-methyl-3-isobutyl-xanthine was aspirated. The cells were then given 8 mL of standard medium and were allowed to differentiatefor an additional 3 days.