The effect of fibronectin on IL-1 alpha, IL-1 beta, tumour necrosis factor-alpha (TNF-alpha), and IL-6 production was investigated with cultured monocytes isolated from human peripheral blood. Monokine concentrations were determined by both ELISA and bioassay. Fibronectin markedly stimulated the secretion of IL-1 alpha, IL-1 beta, TNF-alpha and IL-6 from cultured monocytes in a dose-dependent manner, with the maximal effect apparent within 24 h. Northern blot analysis revealed a marked increase in the abundance of mRNA specific for each monokine on exposure of monocytes to fibronectin. Monoclonal antibodies to the alpha chain of very late antigen (VLA)-5, the beta 1 integrin, the alpha chain of Mac-1, and the beta 2 integrin, as well as the synthetic peptide of GRGDSP (which corresponds to the cell-binding domain of fibronectin), inhibited (> 50%) fibronectin-induced monokine production. Monoclonal antibodies to the alpha chain of VLA-4, and the alpha chain of LFA-1, as well as the synthetic peptide CS-1 (which corresponds to the alternatively spliced connecting segment of fibronectin) and the control peptide GRADSP, had no inhibitory effect on monokine production. A MoAb, R60, that recognizes an epitope of the fibronectin molecule that includes the RGD sequence, inhibited monokine production, whereas the MoAb Y16, which recognizes another epitope of fibronectin not including RGD, did not. These results indicate that fibronectin-induced production of IL-1 alpha, IL-1 beta, TNF-alpha and IL-6 from cultured monocytes is mediated predominantly by interaction of the cell-binding domain of fibronectin with VLA-5, although Mac-1 also may contribute to this effect of fibronectin. Our results indicate that the interaction of fibronectin with integrins may contribute to the cytokine network in inflammatory response.