One hundred forty-two breast cancer patients were evaluated for three functional immunologic parameters: the ability of their lymphocytes to proliferate in response to general T-(phytohemagglutinin) and B-lymphocyte (pokeweed mitogen) stimulators and their ability to proliferate in response to specific autologous tumor antigens. Tests were performed on patient blood specimens collected approximately 2 hours prior to surgery or 2-4 weeks following chemotherapy. T-lymphocyte functional competence was impaired in 83/142 (58%) of the patients, while B-lymphocyte competence was impaired in 34/142 (24%) of these patients. A total of 21/52 (40%) of the patients had lymphocyte immunity against autologous tumor antigen. There were weak associations between the ability of patients' T- and B-lymphocytes to function normally, and their ability to respond to autologous tumor-antigen. There was no relationship of age, tumor burden (clinical or pathological tumor size), extension to skin and/or muscle, or metastasis to any of the three immunological parameters. A relationship (p = 0.0463) between T-lymphocyte competence and pathological nodal status was observed; individuals that were node positive for disease, tended to have impaired T-lymphocyte function. When evaluating T- and B-lymphocyte competence and lymphocytic immunity against tumor antigen in pre- and post-chemotherapy patients, an immunologic rebound (increase in immune parameters shortly after completion of chemotherapy) was observed in some patients. These results demonstrate the utility of measuring these immune parameters in breast cancer patients, their relevance to the natural biology of the disease, and the influence that chemotherapy may have on host immune function.