To assess the role of polymorphisms in the β2-adrenergic receptor gene in the development of obesity and obesity-related metabolic disorders, we analysed Arg16Gly, Gln27Glu, and Thr164Ile polymorphisms in 400 non-obese subjects (body mass index < 27 kg/m²) and 108 obese subjects (body mass index ≥ 27 kg/m²). The Gln27Glu substitution was twice as common in obese subjects as in non-obese subjects (0.14 vs 0.07, p = 0.001, odds ratio 2.14, 95 % confidence interval 1.35–3.41). The frequency of the Glu27 allele was also higher in patients with Type II (non-insulin-dependent) diabetes mellitus than non-diabetic subjects (0.14 vs 0.07, p = 0.001, odds ratio 2.13, 95 % confidence interval 1.34–3.41). Analysis of variance of multiple variables showed an association between 2-h post-load glucose concentrations and body mass index but not with the Glu27 variant, suggesting that the association with diabetes could be secondary to obesity. Obese subjects carrying the variant allele had higher concentrations of serum triglyceride than obese subjects homozygous for the wild type allele (2.68 ± 1.90 vs 1.18 ± 1.15 mmol/l, p = 0.02). Conversely, the frequency of Gly16 homozygotes was lower in obese women when compared with non-obese women (11 % vs 28 %, p = 0.01, odds ratio 0.30, 95 % confidence interval 0.12–0.75), although the association was not present in male subjects. Thr164Ile substitution was not detected in the subjects of this study. These observations suggest that the amino-terminal polymorphisms of the β2-adrenergic receptor gene could be involved in the molecular pathogenesis of obesity and hypertriglyceridaemia, and thereby the development of Type II diabetes mellitus. [Diabetologia (1999) 42: 98–101]