Previous studies have shown that ablation of cranial neural crest results in heart malformations in chick embryos. Cranial neural crest cells populate all of the pharyngeal arches and provide the mesenchymal walls of the aortic arch arteries. Neural crest cells migrate from the pharyngeal apparatus into the outflow region of the heart. However, it is not known which of the pharyngeal arches contribute ectomesenchyme to the developing heart nor has a pattern of distribution in the outflow region been established. In the present study, premigratory presumptive arch neural crest from quail embryos was grafted homotopically onto early chick embryos. On Day 6 of incubation, the chimeric embryos were fixed and processed for histological evaluation. The neural crest providing mesenchyme to pharyngeal arches 1 and 2 was not associated with the developing heart. Neural crest presumptive for arches 3, 4, and 6 was found distributed to the outflow region of the heart. Neural crest from arch 4 contributed the largest number of cells to the developing aorticopulmonary and conotruncal septa. This information indicates that ablations of neural crest presumptive for arches 3, 4, and 6 influence heart development directly while lesions of other areas of cranial neural crest probably influence heart development only secondarily with the primary effects occurring in the pharyngeal arches.