Eighty-two patients with metastatic breast cancer were treated with adriamycin, cyclophosphamide, and 5-fluorouracil (FAC). These patients were divided by randomization into two groups. One was receiving cytostatic drugs only, while another received the identical cytostatic medication plus additional therapy consisting of IV infusions of gamma-radiation-sterilized cells of Propionibacterium granulosum strain KP-45. Metastases were localized in six different sites and/or organs. Multiple parameters for monitoring changes in metastatic lesions and laboratory tests were performed serially in all patients. The addition of P. granulosum to standard (FAC) chemotherapy of metastatic breast cancer influenced metastases in the liver. It also resulted in increased survival time within the observation period. Possible mechanisms of immunomodulating activity of P. granulosum in this disease are discussed.