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To determine whether a common quantitative trait locus (QTL) influences the variation of fasting triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) levels, we used a bivariate multipoint linkage analysis with 654 polymorphic markers in 99 white and 101 black families. The phenotypes were investigated under two conditions: at baseline and after a 20- week exercise training intervention. A maximum genome-wide bivariate LOD score of 3.0 ( p 0.00010) was found on chromosome 12q23–q24, located within the IGF1 gene (insulin-like growth factor 1, at 107 cM) for TG and HDL-C at baseline in whites. This bivariate linkage peak is considerably higher than the univariate linkage results at the same chromosome location for either trait (for TG, LOD 2.07, p 0.00108; for HDL-C, LOD 2.04, p 0.00101). The genetic correlations between baseline TG and HDL-C levels were 0.14 for the residual and 0.33 for the QTL components. Moreover, association analysis showed that TG, HDL-C, and IGF1 are significantly associated ( p 0.04). In conclusion, these results suggest that a QTL on chromosome 12q23–q24 influences the variation of plasma TG and HDL-C levels. Further investigation should confirm whether IGF1 or another nearby gene is responsible for the concomitant variation in TG and HDL-C levels.