Prostate cancer (PCa) and obesity are currently two of the most prevalent health problems in the western world. Some epidemiological studies suggest a connection between PCa and fat intake and obesity. In addition, androgens, which are required for prostate growth and maintenance, as well as being necessary for the beginning stages of PCa, induce lipogenic phenotype and gene expression profile in PCa cells. Furthermore, androgens play a regulatory role in fat cells. We therefore hypothesized that there are common gene expression patterns between prostate and adipocytes. To assess this possibility, we used cDNA microarrays made from a prostate enriched library to identify genes that are commonly regulated by androgens in the PCa cell line LNCaP and during differentiation of 3T3-L1 cells into adipocytes. This screen identified Humanin (HN) and Bax Inhibitor 1 (BI-1) as two such genes, and their expression profiles were verified by quantitative RT-PCR. HN was found to be upregulated during adipogenesis and dose-dependently regulated by androgen in LNCaP cells. BI-1 was only slightly regulated by androgen in LNCaP cells and not regulated during adipogenesis in 3T3-L1 cells. A HN specific antibody was used to detect the predicted 3kD peptide in prostate and adipocyte cell extracts. In both tissues, we identified a peptide of 10 kD which is likely due to post-translational modification of the HN peptide in these tissues. Further studies are needed to assess the functional role of HN in these tissues.