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We examined sources of variability in stature, body mass, and body mass index (BMI) in families of black and white elementary schoolchildren from Philadelphia, Pennsylvania. The sample consisted of 445 black and 379 white children, 7-13 years old, and their parents (total n = 2016). The sample was distributed among 596 nuclear families, each representing an independent pedigree. Maximum-likelihood-based variance decomposition methods were used to simultaneously estimate ethnic group-specific effects of genes, sex, age by sex, and unmeasured environmental factors on stature, body mass, and BMI. Likelihood ratio tests were performed to assess the significance of h2 estimates and differences in