The Pro(12)Ala polymorphism of the peroxisome proliferator-activated receptor-gamma2 gene is associated with insulin sensitivity. Obesity is a major risk factor for insulin resistance, but the association of the Pro(12)Ala polymorphism with body weight has been controversial. Furthermore, obesity may modulate the effect of this polymorphism on insulin sensitivity.The aim of our study was to investigate the effects of the Pro(12)Ala polymorphism on skeletal muscle and adipose tissue glucose uptake (GU) in nonobese and obese subjects.The design was a cross-sectional study.The rates of GU were investigated in 124 (72 nonobese and 52 obese; body mass index cutoff point, 27 kg/m(2)) healthy subjects with the euglycemic hyperinsulinemic clamp. Skeletal muscle and adipose tissue GU and skeletal muscle perfusion were measured using fluorine-18-labeled fluorodeoxyglucose, [(15)O]H(2)O, and positron emission tomography.The rates of skeletal muscle GU were higher in nonobese subjects carrying the Ala(12) allele than in subjects carrying the Pro(12)Pro genotype (P = 0.004), whereas no differences were found in skeletal muscle perfusion between the groups. In contrast, in obese subjects the rates of skeletal muscle GU did not differ between carriers of the Ala(12) allele and carriers of the Pro(12)Pro genotype. No difference in adipose tissue GU was found in either nonobese or obese subjects according to Pro(12)Ala polymorphism.We conclude that the Pro(12)Ala polymorphism modulates skeletal muscle GU differently in nonobese and obese subjects.