In this study we partition the phenotypic correlations between body fat measures and serum levels of hormones with known, or suspected, lipolytic effects into their genetic and environmental components. Using variance decomposition techniques, we are able to estimate the pleiotropic effects of genes and/or shared environmental factors that give rise to the phenotypic correlations previously reported between these traits. We used data from a large sample of randomly ascertained Mexican-American families living in San Antonio, TX. Data were available for 582 individuals in 26 pedigrees. Levels of sex hormone-binding globulin, dehydroepiandrosterone sulfate, insulin, insulin-like growth factor I, total T4, and total T3 were assayed. The measures of body fat accumulation and topography included body mass index, subscapular/triceps ratio, and relative fat patterning index. The results of this analysis demonstrate that significant phenotypic correlations among these traits can arise from three underlying conditions: 1) entirely from shared genetic effects (pleiotropy), 2) entirely from shared random environmental effects, or 3) a combination of both effects. However, we also show that it is possible for significant genetic and environmental correlations to interact in such a way as to produce a phenotypic correlation that itself would not be considered significant.