Human SH-SY5Y neuroblastoma cells were induced to neuronal differentiation by using 12-0-tetradecanoylphorbol-13-acetate (TPA) and retinoic acid (RA). Both treatments rapidly induced long neurites and increased the content of neurofilaments as shown by immunocytochemistry and immunoblotting. Immunoprecipitation and immunoblotting of the culture medium with monoclonal antibodies demonstrated a rapid onset of synthesis and secretion of Mr 280,000 tenascin (Tn) polypeptide with TPA and both Mr 280,000 and 190,000 Tn polypeptides with RA and an increased secretion of extradomain A cellular fibronectin (EDA-Fn) upon both treatments. Upon RA treatment both Tn polypeptides were also found in extracellular matrix preparations of the differentiated cells. A diffuse extracellular Tn immunoreactivity and a distinct cytoplasmic reaction were seen in differentiated cells especially after exposure to monensin to inhibit cellular secretion. Instead, immunoprecipitation experiments suggested that laminin was synthesized by the cells but was not upregulated upon differentiation. Experiments with purified Tn, used to coat the culture substratum, demonstrated that the undifferentiated cells were unable to adhere or spread on Tn but rapidly acquired the spreading capacity upon differentiation with the inducing agents. In immunofluorescence and immunoblotting the undifferentiated cells presented only a faint heterogenous reaction for beta1 integrin (Int) subunit, whereas cells exposed to RA presented a strong reaction for the Int alpha1 and beta1 subunits, hence suggestive of Int alpha1beta1, and for Int alpha(v) subunit. Cells exposed to TPA showed an enhanced immunoreaction for Int alpha2 and beta1 subunits, suggestive of Int alpha2beta1, and for Int alpha(v) subunit. Immunoreactivity for Int alpha(v) located to distinct punctate plaques in the differentiated cells after both inducing agents. The results suggest that Tn is produced by cultured neuronally differentiating cells, and it is accompanied by the acquitance of an adhesion receptor for Tn.