The sex-linked recessive dwarf gene dw was introduced from a broiler strain into lines selected for high (HW) and low (LW) eight-week body weight. Repeated backcrossing of heterozygous males to females from the respective HW and LW lines enabled comparisons between pullets with the Dw and dw alleles in specific genetic backgrounds. The depressive effect of the dw gene on growth was greater in the LW than HW genetic background. Also, the depression was greater for body weight than for skeletal size regardless of line.Dwarf pullets in the LW line consistently matured at older ages than their nondwarf sibs, while in the HW line dwarfs matured about 5 days earlier than their normal sibs in B3 and B4 generations. On a percentage hen-day basis, HW dwarfs produced 3.4% fewer yolks but 4.4% more normal eggs than their nondwarf sibs. Detrimental effects of the dw gene on normal egg and yolk production were evident in the LW line after the F1 generation, suggesting that there may be an optimum body weight for the initiation and efficient production of normal eggs. The data support the hypothesis that dw has a synchronizing effect on ovarian and oviducal functions in populations with excess yolk synthesis and arhythmic ovulation patterns, and a detrimental effect in those populations with optimum ovarian activity. Evidence was obtained to show that the effects of dw on growth and reproduction are largely dictated by specific interactions with the background genotype and the presence of genetic modifiers.