Despite recent advances, controversy continues about the inheritance of the amount and distribution of body fat. We have studied the genetic and 'cultural' (nongenetic) transmission between generations of the body mass index, sum of six skinfold measurements, percentage of body fat, fat mass, fat-free mass, and two indicators of fat distribution. These data were obtained in 1698 members of 409 families, which included the following pairs of family members: spouses, (maximum number of pairs = 348), foster parent-adopted child (322), siblings by adoption (120), first-degree cousins (95), uncle/aunt-nephew/niece (88), parent-natural child (1239), full sibs (370), dizygotic twins (69), and monozygotic twins (87). The total transmissible variance ranged from about 40 percent for the amount of subcutaneous fat to 60 percent for the pattern of subcutaneous fat distribution. Biological inheritance accounted for only 5 percent of the variance for subcutaneous fat and the body mass index, but 20 to 30 percent for the percentage of body fat, fat mass, fat-free mass, and fat distribution. These data suggest that the amount of internal fat is influenced by heredity more than the amount of subcutaneous fat. Furthermore, we consistently found that nongenetic influences are quite important in determining the amount and distribution of body fat in the population. These estimates may differ in the subpopulation of obese individuals.