Although it is well-established that β₁integrins play a functional role in the migration of cranial neural crest cells, little is known about the number or importance of their associated α subunits. Here, we have utilized antisense oligonucleotides (aONs) against various mammalian integrin α subunits to functionally “knock out” integrinsin vitroandin vivo.First, we examined the attachmentin vitroof cranial neural crest cells to fibronectin and laminin in the presence of antisense or reversed-sense oligonucleotides using a quantitative adhesion assay. We found three α integrin aONs that blocked attachment to fibronectin substrates only, one that blocked attachment to laminin substrates only, and one that blocked attachment to both fibronectin and laminin. As expected, an aON to chick β₁integrin reduced attachment to both fibronectin and laminin substrates. These results suggest that there are three or more functionally distinct integrin heterodimers on avian cranial neural crest cells. Second, we examined the ability of aONs against various α integrin subunits to perturb cranial neural crest migrationin vivoby injecting the oligonucleotides into the cranial mesenchyme through which neural crest cells migrate. Those α aONs that inhibited cell attachmentin vitroalso caused neural crest and/or neural tube abnormalities after injectionin vivo.In addition, two aONs that had no effectin vitrodid affect emigration of neural crest cellsin vivo.Immunoprecipitations revealed that some integrin subunits were depleted after treatment with antisense but not reversed-sense oligonucleotides bothin vivoandin vitro.The results suggest that integrin α subunits are required for cranial neural crest cell attachment and emigration.