Leptin is a 16-kDa protein secreted by adipocytes that has been proposed to regulate feed intake in mice, rats, and humans. The present study was designed to characterize porcine leptin structure and expression. Successful RT-PCR resulted in development of a cDNA clone to the full length coding region of porcine leptin. Sequence data demonstrate 85% base homology to rodent, 88% to human, and a 92% homology to the bovine sequence. For assessment of porcine leptin gene expression, total RNA was extracted from the subcutaneous adipose tissue of genetically selected high backfat pigs and from contemporary crossbred swine. Total RNA derived from genetically selected high fat pigs contained 113% higher (P < .05) concentrations of porcine leptin mRNA than total RNA derived from contemporary crossbred pigs. Western blotting was used to evaluate serum levels of porcine leptin in genetically selected high backfat and contemporary, crossbred pigs. Relative levels of porcine leptin in sera from obese swine were approximately 306% higher (P < .05) than levels present in sera from contemporary, crossbred swine. These data indicate that leptin is expressed in pigs, the expressed protein is secreted into the bloodstream, and obese swine express higher levels of leptin mRNA and protein than nonobese swine at similar body weight.