Polybrominated diphenyl ethers (PBDEs) are lipophilic flame‐retardant chemicals found in many consumer products and increasingly in human tissues. The purpose of this study was to elucidate whether exposure to PBDEs in conjunction with a high‐fat/high‐sugar (HF) diet will predispose male Wistar rats to obesity. Twenty four rats were fed either a control (C) or HF diet, and gavaged with either 18 mg/kg PBDEs (+) or corn oil (‐) daily for 4 weeks (n=6 per group). Body weight and food intake were measured three times per week. At 3 weeks, 24‐hr whole body metabolism was measured. At 4 weeks, blood was sampled for plasma thyroid hormone concentration (T4), epididymal fat pads were removed and weighed, and adipocytes were isolated. Adipocyte size and lipolytic response to adenosine deaminase and varying concentrations of isoproterenol over 90 min were measured. Findings revealed that there were no significant differences in lipolysis with ADA or isoproterenol. A slight but significant increase in % body weight change was seen in + vs. ‐ rats. HF rats consumed 9% more kcals than C rats over the 4 week study (P<0.05). T4 levels decreased by 83% in + vs. ‐ rats (P<0.05). Whole body metabolism results are pending. PBDEs cause an increase in body weight and reduction in T4 without affecting adipocyte size and lipolytic sensitivity; the mechanism by which this occurs is unknown. Supported by Agric. Expt. Stn. Grant NH 00485.