OBJECTIVE To investigate the association of the Trp64Arg polymorphism of the β3-adrenergic receptor gene with NIDDM and the features of insulin resistance syndrome in subjects from eastern Finland. RESEARCH DESIGN AND METHODS We determined the prevalence of the Trp64Arg polymorphism of the β3-adrenergic receptor gene by restriction fragment length polymorphism analysis in 110 patients with NIDDM (54 men and 56 women, age 63 ± 1 years, BMI 30.4 ± 0.5 kg/m2), in 183 patients with features of insulin resistance syndrome (103 men and 80 women, age 44 ± 0 years, BMI 31.1 ± 0.4 kb/m2), and in 82 normoglycemic control men (age 54 ± 1 years, BMI 26.3 ± 0.4 kg/m2). RESULTS The allele frequency of the Trp64Arg polymorphism of the β3-adrenergic receptor gene was similar in patients with NIDDM, in patients with insulin resistance syndrome, and in control subjects (0.08, 0.07, and 0.07, respectively; NS). In addition, this polymorphism was not associated with low resting metabolic rate, abdominal obesity, increased lipid oxidation, hypertension, or earlier development of NIDDM as previously described. Furthermore, in 82 normoglycemic male control subjects the Trp64Arg polymorphism was not associated with insulin resistance evaluated by the euglycemic-hyperinsulinemic clamp. CONCLUSIONS The Trp64Arg polymorphism of the beta β3-adrenergic receptor gene is unlikely to be a major genetic predisposer to NIDDM or insulin resistance syndrome in subjects from eastern Finland.