Experiments were conducted to determine the quantitative requirement of vitamin D3 for the maximum performance of broiler breeder hens and to relate the effects of the various levels of vitamin D3 in the maternal diet with the performance, tibia ash, tibial dyschondroplasia (TD) and Ca deficiency rickets incidence of the progeny fed a diet deficient in vitamin D3 or diets supplemented with various levels of vitamin D3, Ca, or 25-hydroxycholecalciferol. A second set of experiments were conducted to determine the relative biological value of 25- hydroxycholecalciferol in comparison to D3 for broiler breeder hens and to relate the two D sources in the maternal diet with the performance, tibia ash and leg abnormalities of the progeny fed diets deficient in vitamin D3 or supplemented with 1,100 IU of vitamin D3 per kg of diet. Analyses of the data indicate a requirement of approximately 1,400 and 2,800 IU of vitamin D3 per kg of feed for the maximum performance of broiler breeder hens from 25 to 36 and 37 to 66 weeks of age, respectively. Increasing the level of vitamin D3 in the maternal diet was effective in improving performance, tibia ash and in reducing TD andCa rickets incidence of the progeny fed diets deficient in vitamin D3 or diets with various levels of vitamin D3, Ca or 25- hydroxycholecalciferol. The results from these studies, although not always statistically significant for tibia ash, TD and Ca rickets incidence throughout the different experiments with the progeny, suggest that the requirement of broiler breeder hens to produce the heaviest and healthiest chicks is considerably higher than the requirement for maximum egg production of the hens and higher than the NRC (1994) or Scott et al. (1982) recommendations, especially when birds are raised in environments having almost no measurable UV light. The relative biological value of 25- hydroxycholecalciferol in relation to vitamin D3 depends on the level tested. When comparing vitamin D sources, 25- hydroxycholecalciferol has greater relative biological value than vitamin D3 only at very low levels of supplementation.