Using a monoclonal antibody raised against human platelet thrombospondin, we found anti-thrombospondin immunoreactivity in the extracellular matrix of avian embryos, coincident with the ventral pathways followed by trunk neural crest cells. To confirm that the antibody recognized thrombospondin-1 and to determine the tissue of origin of the thrombospondin matrix, a thrombospondin-1 cRNA probe was used for whole mount in situ hybridization. This probe revealed thrombospondin-1 mRNAs in the developing myotome before and during neural crest cell migration. The effect of thrombospondin-1 on neural crest cell migration, morphology, and adhesion was assayed in vitro. Quail trunk neural crest cells cultured on 4 microg/ml of thrombospondin-1 migrate at 1.14 +/- 0.54 microm/min, which is significantly greater than the rate of cell migration on tissue culture plastic. Using a shaker-based adhesion assay, a significantly greater number of neural crest cells remain attached to dishes coated with 4 microg/ml of thrombospondin-1 than to tissue culture plastic alone. The number of neural crest cells that remain attached to 4 microg/ml of thrombospondin-1 is similar to the number that remain attached to dishes coated with 10 microg/ml of fibronectin. These observations indicate that neural crest cells migrate through a thrombospondin-filled extracellular matrix, and that thrombospondin-1 promotes neural crest cell migration and adhesion. Thus, thrombospondin-1 is the first somite-derived extracellular matrix molecule with properties consistent with a role in the promotion of migration into the anterior somite, as opposed to the repulsion of neural crest cells from the posterior half of the somite.