The primary fibronectin gene transcript is alternatively spliced in three regions, designated EIIIA, EIIIB and IIICS. While the functions of the EIIIA and EIIIB domains are still to be established, either end of the IIICS domain contains the cell-binding sites CS1 and CS5 recognised by the integrin VLA-4 which is present on mononuclear cells. We have determined the effects of three cytokines upon fibronectin mRNA and IIICS splice variants in four cultured human cell lines using Northern hybridisation and PCR. In the cell line CAKI-2, interleukin 1 beta, Platelet-derived growth factor BB and transforming growth factor beta 1 all increased mRNA splice variants where the CS1 and CS5 regions were removed. This cytokine-induced change would lead to a decrease in the CS1 and CS5 cell binding sites within the extracellular matrix. All the changes in spliceosome function increase use of downstream 3' splice acceptor sites and may represent use of a single common pathway by three different cytokines.