CYP2B6 metabolizes xenobiotic and endobiotic compounds, including drugs, environmental toxicants, steroids, and polyunsaturated fatty acids (PUFAs). Studies indicate that the constitutive androstane receptor (CAR), a potent inducer of Cyp2b has antidiabetic effects, recognizes increased concentrations of PUFAs, and regulates lipid metabolism potentially through induction of CYPs. Several CYPs hydrolyze or epoxygenate PUFAs, which is cardioprotective, dilates blood vessels and alters inflammation and pain. We examined the metabolism of PUFAs by hCYP2B6 baculosomes exposed to 30 µM linoleic acid (LA) or 25 µM arachidonic acid (ARA). CYP2B6 baculosomes increased concentrations of the proinflammatory LA metabolites 13-HODE, 9,10-DiHOME, and 20-HETE, and decreased concentrations of the anti-inflammatory metab-olite Resolvin D1/2 indicating a role for CYP2B6 in LA metabolism and inflammation. Few metabolites were formed from incubations with ARA when comparing -null and CYP2B6 containing baculosomes. To further investigate the role of CYP2B in lipid metabolism, a Cyp2b9/10/13-null mouse model was produced, lacking hepatic Cyp2b members. Wildtype (WT) and Cyp2b9/10/13-null mice were fed a normal diet (ND) or a 60% by weight high-fat diet (HFD). Cyp2b9/10/13-null male mice fed a HFD for 10 weeks weighed 15% more than their HFD-fed WT counterparts, mainly due to increased white adipose tissue. Liver samples from the WT and Cyp2b9/10/13-null mice were used to determine lipid metabolism by LC-MS/MS and examined for free fatty acids and the phospholipid species of LA, ARA, and docosahexaenoic acid (DHA). Metabolites of LA such as LysoPC 18:2 and PIP3 38:2 decreased 46% and 100% respectively, and the ARA metabolite LysoPE 20:4 was reduced 45% in Cy2b9/10/13-null mice. Conversely, the anti-inflammatory PC 36:2-CH3/PG 36:3 species of LA (29%), PC 40:6-CH3/ PE 42:6 of DHA (52%) and PC 38:4-CH3/CL 84:21 of ARA (75%) increased in Cyp2b9/10/13-null mice. This data indicates a pro-inflammatory, but anti-obesity role of Cyp2b. Thus, toxicants that inhibit CYP2B6 may exacerbate obesity while reducing inflammation. RNAseq was recently performed on the livers from the HFD-fed WT and Cyp2b910/13-null mice. Changes in gene expression, particularly for fatty acid metabolism, gluconeogenesis, lipogenesis, insulin signaling, and inflammation will be evaluated. In conclusion, the Cyp2b enzymes are involved in fatty acid metabolism and obesity; therefore chemical inhibition of these enzymes may exacerbate obesity.