A method was described for preparation of mouse bone marrow primary cultures, using the embryo/uterus growth factor to stimulate bone marrow cells, for sister chromatid exchange (SCE) and chromosomal aberration studies that could be used for in-vivo and partial in- vivo comparison and in-vitro genotoxicity assays. The steps of the procedure included the following: preparing the whole uteri extract; preparing reagents and media; preparing the bone marrow cells; setting and harvesting the cultures; preparing and staining the slides for SCE differentiation; and staining the slides for chromosomal aberration analysis. Mice were killed by cervical dislocation, tibia and femora were isolated, bone marrow was flushed with Ham's F12 medium, and for SCE studies, 5-bromo-2'-deoxyuridine was added to the cultures for 24 to 28 hours. Culture cycles lasted for approximately 12 to 14 hours. In the present method, animals could be exposed to single or multiple doses of the test compounds, and results obtained pertaining to metabolic activation could be extrapolated to humans. The system was used to compare SCEs in bone marrow cells after 5-bromo-2'-deoxyuridine incorporation in culture and those after exposure to 20mg/kg cyclophosphamide (50180) followed by cell culturing. Chromosomal aberrations were also studied employing this method.