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Involvement of genetic factors in determining bone mineral density (BMD) is doubtless. However, the exact nature of the genes governing BMD variation and sources for genetic determination of BMD of different parts of bone (compact and cancellous) have not been completely studied. The results of the complex segregation analyses performed in our previous study (Livshits et al. 1996) on a Turkmenian sample strongly support the hypothesis that a single Mendelian locus has a large effect on BMD. The parameter estimates for both types of bone tissue were so similar that we could assume a common gene effect for BMD variation of cancellous and compact bone. The objectives of the present study are to test again the possibility of major gene control of BMD in a different ethnic sample of pedigrees, namely, the Chuvasha. In addition, we report here the results of a bivariate segregation analysis of compact and cancellous BMD performed in both the Turkmenian and the Chuvasha samples of pedigrees. The results of the present study closely resemble the results obtained on the Turkmenian pedigrees. Likewise, the major finding of the present study is that there is a significant major gene effect on both compact and cancellous BMD; polygenic hypotheses were clearly rejected. Moreover, the results of the bivariate segregation analysis in both the Chuvasha and Turkmenian samples were similar. They lead to acceptance of the hypothesis that there is a single major locus with pleiotropy to both compact and cancellous bone.