Lymphocyte adhesion to components of extracellular matrices (i.e. fibronectin) is important for their proper localization in tissues and inflammatory sites. We have studied the attachment of the human cell line HUT-78 (mature T lymphocytes) to fibronectin and to several tryptic fragments of fibronectin. HUT-78 cells effectively adhered to surfaces coated with two Hep II domain-containing fragments of 38,000 and 58,000 MW derived from the A and B chains of fibronectin, respectively. Cells also bound to an 80,000 MW fragment containing the RGDS sequence of fibronectin. Cell adhesion to the 38,000 MW fragment was completely inhibited (100%) by cell preincubation with the soluble 38,000 MW fragment; it was partially inhibited (30-37%) by preincubation with the 58,000 MW fragment or with a synthetic peptide CS-1, comprising the first 25 amino acid residues of the alternatively spliced connecting segment (IIICS), which is present in the A chain of fibronectin and in the 38,000 MW fragment. Cell preincubation with RGDS-containing synthetic peptides or with the 80,000 MW fragment, did not affect attachment to 38,000 MW-coated surfaces. Moreover, preincubation of HUT-78 cells with 38,000 MW fragment had no effect on cell adhesion to 80,000 MW-coated wells, while preincubation with 80,000 MW fragment completely inhibited cell attachment to these surfaces. These results strongly suggest the involvement of two different cell surface receptors which recognize the Hep II/IIICS site and the RGDS site independently. Preincubation with either 38,000 or 80,000 MW fragments prevented cell attachment to fibronectin, indicating that adhesion to the intact molecule requires interaction with both regions. Therefore T-lymphocyte adherence to fibronectin-containing matrices may be regulated by the co-expression of both receptors at the cell surface.