Much of the classic body composition research used a two-component (2C) model to estimate percent body fat (BF%) from body density determined by underwater weighting (U-BD). Dual-energy X-ray absorptiometry (DXA), a three-component model, is becoming the laboratory method of choice to measure BF%. PURPOSE: To compare the effects of race and body mass index (BMI) on BF% measured by U-BD, 2-C and DXA methods. METHODS: The subjects included white (W) and African-American (AA) men and women from the HERITAGE family (n=385) and TIGER studies (n=826). The young adults ranged in age from 17 to 35 y. The subjects underwent in an exercise intervention and had their BF% measured 1 to 3 times over 9 months. The BF% of the TIGER subjects was measured by DXA. Sex and race specific 2-C equations were used to calculate BF% from U-BD of the HERITAGE subjects. Linear mixed models (LMM) regression was used to analyze the all observations, which were 1,266 for women and 820 for men. The independent variables were BMI, BF% method (2-C vs. DXA) and race (W vs. AA) and the dependent variable was BF%. The men and women‘s data were analyzed separately. RESULTS: The LMM results for women and men were similar. A significant BMI by method showed that below a BMI of about 25 kg/m2, the Siri BF% for a given BMI was lower than DXA BF%, but above 25 kg/m2 the 2-C BF% was higher than DXA BF%. Adding race to the LMM improved model fit (p <0.001) for both men and women. Graphic examination of the trends showed that for a given BMI, the DXA BF% of AA men was about 4.6% lower than W. The DXA BF% of AA women was nearly 2% lower than W women. CONCLUSIONS: These results showed there is both a race and method effect for young men and women when using the DXA and U-BD, 2-C laboratory methods to measure BF%. The method effect is a function of BMI level. Supported by NIH Grant DK062148 and HL45670