The obese (ob) gene isolated from ob/ob mice in 1994 is expressed specifically in adipose tissue. The gene product, leptin, regulates food intake, energy expenditure and puberty. Reported herein is a 2477 bp mRNA sequence for the pig obese gene, which includes the complete coding sequence. Two different ob cDNAs were identified, which differed by the inclusion or exclusion of a single glutamine codon at position + 49 of the protein sequence. The pig obese gene encodes a 4.5 kb mRNA transcript, which is specific to adipose tissue. Southern blot analysis of fat and lean pigs showed a DNA polymorphism related to the lean phenotype. Differences in leptin mRNA levels showed that fat pigs have a higher level of leptin mRNA than lean pigs. These findings indicate that pig leptin expression can be associated with subcutaneous fat accumulation in pigs. Key words: Obese gene, polymorphism, mRNA, expression, swine, leptin