A level of X-ray induced mitotic disturbances in the cells of the bone marrow of male mice was studied under the modifying influence ofchemosignals from isolated adult female mice of the CBA line. It has been shown that the frequency of chromosomal aberrations in irradiated (4 Gr) males after exposing them for 24 hours on bedding soiled with female chemosignals is lower than in irradiated males in cages with clean bedding. The mechanisms and importance of the antimutagenic effect of female house mouse chemosignals are discussed.