The frequency of sister chromatid exchanges (SCE) in vivo and chromosome aberrations and/or alterations were analyzed from the bone marrow cells of the treated dbrB tumor-bearing DBA/1J inbred mouse host. The results were compared with analogous data obtained from the bone marrow cells of untreated tumor-bearing mice for evaluation of the "indirect," i.e., somatic stress, effect on the normal host cells following triple-agent therapy intended for a mammary adenocarcinoma. Misonidazole (MIS), which is a known radiosensitizing drug, microwave hyperthermia (delta), and X-radiation (X) were used as therapeutic agents. Significant (P less than 0.05) numbers of SCE were induced in the bone marrow cells of the mice whose tumors received these triple-agent treatments (MIS + delta + X) simultaneously as compared with values of SCE per cell noted in bone marrow cells of untreated tumor-bearing control mice. The highest number of chromosome aberrations and alterations, including an increase in heteroploidy, was also noticed in the bone marrow cells of the mice whose tumors were treated simultaneously with MIS + delta + X. The triple-agent therapy on dbrB tumor also resulted in an unusually high polyploid metaphase plate in the bone marrow cell consisting of 320 chromosomes, indicating that this mode of therapy may act directly on the genetic material of the tumor-bearing host cells, inducing cytogenetic abnormalities as a side effect.