The expression patterns of PPAR beta/delta have been described, but the majority of these data are based on mRNA data. To date, there are no reports that have quantitatively examined the expression of PPAR beta/delta protein in mouse tissues. In the present study, a highly specific PPAR beta/delta antibody was developed, characterized, and used to examine tissue expression patterns of PPAR beta/delta. As compared to commercially available anti-PPAR beta/delta antibodies, one of six polyclonal anti-PPAR beta/delta antibodies developed was significantly more effective for immunoprecipitation of in vitro-translated PPAR beta/delta. This antibody was used for quantitative Western blot analysis using radioactive detection methods. Expression of PPAR beta/delta was highest in colon, small intestine, liver, and keratinocytes as compared to other tissues including heart, spleen, skeletal muscle, lung, brain, and thymus. Interestingly, PPAR beta/delta expression was localized in the nucleus and RXR alpha can be co-immunoprecipitated with nuclear PPAR beta/delta. Results from these studies demonstrate that PPAR beta/delta expression is highest in intestinal epithelium, liver, and keratinocytes, consistent with significant biological roles in these tissues. (C) 2008 Elsevier Inc. All rights reserved.