A murine monoclonal antibody, VM-1, which binds to basal cells of normal human epidermis, reduces the ability of human squamous cell carcinoma cells (SCL-1) derived from the skin to attach and spread on collagen by about 50% and causes cell rounding. Similar effects have been previously shown using normal human keratinocytes. The attachment of cell lines derived from human lung squamous cell carcinomas (SW1271 and SW900), melanoma A375, glioblastoma 126, and fibrosarcoma HT1080 is also inhibited by this antibody. VM-1 antibody does not bind to normal human fibroblasts, benign nevus cells, or the human B-cell-derived line 8866. VM-1 antibody inhibits the growth of SCL-1 cells in vitro as measured by cell numbers and [3H]thymidine ([3H]TdR) incorporation. It is not cytolytic in the presence of complement as measured by 51Cr release. Repeated treatment of SCL-1 cells with VM-1 antibody significantly reduces the proportion of SCL-1 cells that attach to collagen. In addition, after treatment of SCL-1 cells with VM-1 antibody, several proteins can no longer be demonstrated by gel electrophoresis of the cell-free supernatant. The VM-1 antibody effect on attachment and spreading is partially reversed by pretreatment of the collagen surface with laminin and fibronectin, but not with the carbohydrates chondroitin-6-sulfate or hyaluronic acid or with the protein lysozyme. By fluorescence staining, the antigen recognized by VM-1 antibody is membrane-bound and Triton X-100 extractable. The VM-1 antigen is excluded from Bio-Sil TSK-400 and sediments at about 10.5 S. It has a covalent molecular weight on the order of 10(6). Proteinase K digestion produces VM-1 antibody reactive fragments, assumed to be polysaccharides, with a polydisperse molecular weight distribution in the range 5000 to 30,000. The VM-1 antigen is partially lost from solution on boiling and is no longer detectable in the aqueous or organic phase after chloroform-methanol extraction. The properties of the VM-1 antigen are consistent with those of a proteoglycan involved in attachment and spreading of keratinocytes and certain tumor cells on collagen.