Availability of a chemically defined chemoattractant (fMLP) and of appropriate monoclonal antibodies may permit local manipulation of the inflammatory response to human tumors. fMLP has been conjugated with two monoclonal antibodies (OC125 and OC133) which react with human ovarian carcinomas. Conjugates retained the ability to bind to a human ovarian carcinoma line (OVCA433) judged by indirect immunofluorescence and by radioimmunoassay. The fMLP conjugate was maximally chemotactic for human blood monocytes and human peritoneal macrophages at protein concentrations of 300-900 micrograms/ml. Conjugates stimulated chemotaxis rather than chemokinesis. After incubation with an fMLP-antibody conjugate, antigen positive OVCA433 cells released chemotactic activity and attracted monocytes in vitro, whereas an antigen-negative ovarian cell line failed to do so. As monocytes can be important effectors of antibody dependent cell mediated cytoxicity, fMLP conjugates might increase monocyte concentrations at tumor sites and potentiate serotherapy for certain human neoplasms.