Immunoelectron microscopy was employed to detect laminin and fibronectin cell surface expression on five Ewing's sarcoma lines plus a normal fibroblast line as control. Monospecific antibodies to both glycoproteins were detected on tumour cell and fibroblast layers with colloidal gold--protein A conjugates. All five tumour lines were positive for fibronectin and/or laminin, whereas the fibroblast line expressed fibronectin only, as expected. Fibronectin displayed a dense granular pattern, typically in the cell-cell and cell-matrix adhesion areas; laminin displayed a punctate pattern. 3H-leucine metabolical labelling was also used to demonstrate laminin and fibronectin synthesis. The labelled proteins released in the culture media were separated by molecular weight on SDS-PAGE and identified by immunoprecipitation with the monospecific antibodies. The results substantiated the immunoelectron microscopy data. These findings indicate that Ewing's sarcoma lines produce a complex extracellular matrix including fibronectin and laminin, in addition to the collagens described by other workers. Histogenetic classification of this tumour in terms of extracellular matrix proteins synthesis is thus more difficult than has been supposed. The same complexity must also be borne in mind when using the matrix components as an aid to Ewing's sarcoma differentiation from other childhood tumours.