Because of their distribution and known ability to promote neuronal adhesion, it has been proposed that N-CAM and N-cadherin are involved in the formation of the nervous system. Here, we examine the expression of these molecules during the initiation and cessation of trunk neural crest cell migration during the formation of the peripheral nervous system. Whereas other neural tube cells express N-cadherin, the dorsal neural tube containing neural crest precursors has little or no N-cadherin immunoreactivity. In contrast, N-CAM is expressed in the dorsal neural tube and on early migrating neural crest cells, from which it gradually disappears during migration. Both N-CAM and N-cadherin are absent from neural crest cells at advanced stages of migration. As neural crest cells cease migration and condense to form dorsal root and sympathetic ganglia, N-cadherin but not N-CAM is observed on the forming ganglia, identified by neurofilament expression and the aggregation of HNK-1 reactive cells. The results demonstrate that the absence of N-cadherin correlates with the onset of neural crest migration and its reappearance correlates with cessation of migration and precedes ganglio-genesis. © 1992 Wiley-Liss, Inc.