Corynebacterium parvum was administered to sixteen patients with malignant tumors submitted to repeated chemotherapy courses. A total of 428 injections of C. parvum at a dose of 3.5 mg/m2 in weekly, biweekly and monthly administration was given between the chemotherapy courses. Injection of C. parvum was followed by fever and local pain in 15/16 patients. Three patients presented a local ulceration during the initial period of weekly injections. Splenomegaly was observed after the second month of treatment, peripheral and bone-marrow monocytic infiltration after the second month. The decreased lymphocyte stimulation by PHA observed during the first two months was followed by an increased response. Cutaneous reactions to three antigens increased progressively in most patients and negative pre-treatment tests became positive after treatment.