This study describes migrating cranial neural crest cells and the microenvironment through which they migrate in chick embryos. Just prior to and during cell migration, an extensive fibrillar meshwork is observed, particularly on the outer surface of the neural tube and the inner surface of the ectoderm. This meshwork in general had a random orientation. This suggested to us that the meshwork does not provide a directive vector for cell migration but rather a substratum to promote or enhance crest cell filopodial attachment as the cells migrate. Much remains to be done in characterizing the composition of this meshwork. Based on other studies in which a smiliar meshwork has been observed, it is not unreasonable to consider it to be partly collagenous. Another major component in the relatively cell-free space through which avian crest cells migrate is hyaluronic acid. The migrating crest cells are characteristically bipolar and are generally oriented in the direction of migration, although little is known about the actual mechanism of motility. Alterations in the migrating cell or in the environment through which it migrates may interfere with normal craniofacial morphogenesis, as discussed elsewhere in this volume by Johnston and Sulik.