The ligand specificity of the integrin cell adhesion receptors probably determines the ability of specific integrins to promote tumor cell proliferation and metastasis. Therefore, we compared the expression of integrin αvβ3, a promiscuous receptor that binds with high affinity to numerous cell matrix proteins, with the expression of integrin αvβ5 and the integrin β1 subunit (which pairs with multiple α subunits) in neuroblastic tumors at various stages of differentiation. Undifferentiated neuroblastoma tumors rapidly invade and metastasize, whereas ganglioneuroblastomas rarely metastasize. Differentiating neuroblastomas are associated with an intermediate prognosis. Paraffin sections of neuroblastic tumors at various stages of differentiation obtained at biopsy from 17 patients were hybridized with antisense integrin subunit-specific αv, β3, β1, and β5 riboprobes. All neuroblastic tumors and seven adrenal glands obtained at autopsy were analyzed immunohistochemically with antibodies directed toward the αv, β3, β1, and β5 subunits. The αv subunit was expressed in neuroblastic tumors independent of the stage of differentiation, although mRNA and protein expression were generally weak in ganglioneuroblastomas, and was also detected in adrenal gland medullae. The β1 subunit was detected in most neuroblastic tumors independent of the stage of differentiation as well as in adrenal gland medullae. In contrast, the β3 subunit, which was not expressed in adrenal gland medullae, was expressed at the protein and mRNA levels in undifferentiated neuroblastomas (six of seven and seven of seven, respectively) but was not expressed in neuroblasts or ganglion cells in ganglioneuroblastomas (one case weakly positive out of five). The β5 subunit was expressed at the protein (five of five) and mRNA (four of five) levels in the ganglion cells of ganglioneuroblastomas and, although mRNA for this subunit was detectable in undifferentiated tumors, the protein was not detectable. The expression of integrin αvβ3 in undifferentiated neuroblastomas may contribute to the rapid growth of these tumors and their tendency to metastasize.