Ablation of various regions of premigratory trunk neural crest which gives rise to the sympathetic trunks was used to remove sympathetic cardiac innervation. Neuronal uptake of [3H]-norepinephrine was used as an index of neuronal development in the chick atrium. Following ablation of neural crest over somites 10–15 or 15–20, uptake was significantly decreased in the atrium at 16 and 17 days of development. Ablation of neural crest over somites 5–10 and 20–25 caused no decrease in [3H]-norepinephrine uptake. Removel of neural crest over somites 5–25 or 10–20 caused approximately equal depletions of [3H]-norepinephrine uptake in the atrium. Cardiac norepinephrine concentration was significantly depressed following ablation of neural crest over somites 5–25 but not over somites 10–20. Light-microscopic and histofluorescent preparations confirmed the absence of sympathetic trunks in the region of the normal origin of the sympathetic cardiac nerves following neural crest ablation over somites 10–20. The neural tube and dorsal root ganglia were damaged in the area of the neural-crest ablation; however, all of these structures were normal cranial and caudal to the lesioned area. Development of most of the embryos as well as the morphology of all of the hearts was normal following the lesion. These results indicate that it is possible to produce sympathetically aneural hearts by neural-crest ablation; however, sympathetic cardiac nerves account for an insignificant amount of cardiac norepinephrine. The adrenal medulla is the most likely source of cardiac norepinephrine in sympathetically aneural hearts.