A twin-based comparative study on the genetic influences in metabolic endophenotypes in two populations of substantial ethnic, environmental, and cultural differences was performed. Design and Methods: Data on 11 metabolic phenotypes including anthropometric measures, blood glucose, and lipids levels as well as blood pressure were available from 756 pairs of Danish twins (309 monozygotic and 447 dizygotic twin pairs) with a mean age of 38 years (range: 18-67) and from 325 pairs of Chinese twins (183 monozygotic and 142 dizygotic twin pairs) with a mean age of 40.5 years (range: 18-69). Twin modeling was performed on full and nested models with the best fitting models selected. Results: Heritability estimates were compared between Danish and Chinese samples to identify differential genetic influences on each of the phenotypes. Except for hip circumference, all other body measures exhibited similar heritability patterns in the two samples with body weight showing only a slight difference. Higher genetic influences were estimated for fasting blood glucose level in Chinese twins, whereas the Danish twins showed more genetic regulation over most lipids phenotypes. Systolic blood pressure was more genetically controlled in Danish than in Chinese twins. Conclusions: Metabolic endophenotypes show disparity in their genetic determinants in populations under distinct environmental conditions.