A new cell line from a sporadic Wilms' tumor was established and extensively characterized. In nude mice, the tumor cells rapidly formed tumors which, in histological characteristics and extracellular-matrix (ECM) composition resembled sarcomatoid Wilms' tumor. The tumor cells produced B chains of laminin, but no A chain, and laminin was deposited into the ECM in a punctate pattern typical of sarcomatoid tumors. Strong expression of tenascin was detected within the stromal ECM of the tumors. Species-specific antibodies reacting either with human or with mouse tenascin showed that tenascin was exclusively derived from mouse host cells. The human Wilms' cell line thus induced a strong stromal response with increased deposition of tenascin. The cell line may be useful for studying the behavior of sarcomatoid Wilms' tumor cells and for identifying factors that stimulate synthesis of tenascin.