To evaluate if leptin's mitogenic action in androgen-resistant prostate cancer cells is linked to proliferative signaling through activation of the MAPK signaling pathway, DU145, PC-3, and LNCaP cells were treated with leptin and phosphorylation of p42/44 MAPK (ERK1/2), a downstream component of MAPK pathway was measured by Western blotting using phosphospecific antibodies. This evidence concerns the gene LEP and prostate carcinoma.