Obese (ob) gene expression in abdominal subcutaneous adipocytes from lean and obese humans was examined. The full coding region of the ob gene was isolated from a human adipocyte cDNA library. Translation of the insert confirmed the reported amino acid sequence. There was no difference in the sequence of an reverse transcription PCR product of the coding region from five lean and five obese subjects. The nonsense mutation in the ob mouse which results in the conversion of arginine 105 to a stop codon was not present in human obesity. In all 10 human cDNAs, arginine 105 was encoded by CGG, consequently two nucleotide substitutions would be required to result in a stop codon. To compare the amount of ob gene expression in lean and obese individuals, radiolabed primer was used in the PCR reaction with beta-actin as a control. There was 72% more ob gene expression (P < 0.01) in eight obese subjects (body mass index, BMI = 42.8 +/- 2.7) compared to eight lean controls (BMI = 22.4 +/- 0.8). Regression analysis indicated a positive correlation between BMI and the amount of ob message (P < 0.005). There was no difference in the amount of beta-actin expression in the two groups. These results provide evidence that ob gene expression is increased in human obesity; furthermore, the mutations present in the mouse ob gene were not detected in the human mRNA population.