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Sibling resemblance and heritability of seven strength (right and left grip, push, pull) and motor performance (dash, jump, throw) variables (age-corrected) were studied in 114 Black and 101 White sibling pairs aged 6 to 12 years from Philadelphia (U.S.A. ). There were no differences in the sibling correlations by race, but brothers tended to resemble one another more than sisters on most of the strength and performance items. Body weight, difference in age between members of a sibling pair, and measurement reliability were significant factors affecting the sibling correlations in strength and motor performance. At face value, heritabilities of strength and performance varied from 22% (jump) to 58% (right grip), not markedly different from the more conservative estimates obtained by holding body weight constant: 17% (pull) to 48% (throw). Of the seven items, heritabilities of the grip strengths and softball throw were highest and varied the least among several models, suggesting a greater genetic basis for these items than for the others.