Tenascin is an extracellular matrix glycoprotein consisting of six disulfide linked subunits with molecular masses of 190-250 kDa. The cDNAs of chicken, mouse and human tenascins were cloned and their amino acid sequences were determined. Molecular analysis of the tenascin gene revealed that it contains a region homologous to the fibrinogen gene, and repetitive sequences of the type III fibronectin and epidermal growth factor genes. Several isoforms of the tenascin gene as splicing variants have also been found. Culture studies have shown that tenascin has multiple functions including cell attachment and detachment, promotion and inhibition of neural crest cell migration, cell growth stimulation and hemagglutination. Immunohistochemistry of a variety of tissues, both normal and abnormal, from various animals has shown that the distribution of tenascin is characteristic, and spatially and chronologically restricted. Immunoreactive tenascin was demonstrated in the dense mesenchyme present around growing epithelia during embryogenesis and oncogenesis. Besides its oncofetal expression, tenascin was also found in many tissues with inflammation such as healing wounds, regenerating tissue and irritated tissue. These findings suggest that tenascin probably functions as a homeostatic factor in the repair of tissue perturbation.