C-57 BL/6 mice with Lewis lung carcinoma were treated 2 weeks after tumor implantation with local microwave hyperthermia (2450 MHz, tumor temperature 43.5 degrees C, 30 min) and/or intratumoral or intraperitoneal injection of 1 mg cell walls of Propionibacterium granulosum KP-45. Tumor growth, survival time of the animals, and the delayed skin hypersensitivity to oxazolone were followed up, as well as the 3H-thymidine uptake of tumorous tissues and the number of lung metastases. The combined treatment of microwave hyperthermia with immunomodulating P. granulosum KP-45 resulted in significantly stronger inhibition of tumor growth than with each of these methods alone. The number of lung metastases could be significantly lowered, and the skin reactivity to oxazolone remained enhanced during the whole observation period (over 70 days after tumor implantation). The implications of the test observation are discussed.