The Pro12Ala polymorphism of the peroxisome proliferator-activated receptor gamma 2 (PPARγ2) gene and adiponectin, a protein secreted from adipose tissue, have been associated with insulin sensitivity. The present study demonstrates that in Finnish servicemen who were on a high-caloric diet for 6 mo only subjects with the Ala 12 allele of PPARγ2 had a significant increase in adiponectin levels with weight loss induced by heavy exercise. This study demonstrates an interaction of genetic and environmental factors in the regulation of serum adiponectin concentrations.