Removal of premigratory neural crest over somites 1 through 3 in chick embryos has been shown previously to result in a significant incidence of persistent truncus arteriosus. In the present study, single somite-length pieces of premigratory neural crest were removed unilaterally at slightly different embryonic ages. These lesions resulted in a number of different heart defects. Two defects, ventricular septal defect and double outlet right ventricle, were significantly correlated with the location of neural crest removed. The stage at which the ablation was performed was important in determining the incidence but not the type of defects.