In this investigation, rats subjected to swim stress showed within 24 hours significant increases in both the level of chromosome aberrations and Sister Chromatid Exchanges (SCEs) in bone marrow cells. The generality of cytogenetic damage by behavioral stressors was demonstrated by exposing rats to both cold-and warm-water forced swims, to white noise, and to continuous or intermittent inescapable foot shock stress (IFS). The induction of chromosome aberrations and SCEs, to differing degrees, by stressors that differ both quantitatively and qualitatively, demonstrates that this is a general phenomenon of stress. The use of an additional measure, unscheduled DNA Synthesis (UDS) showed that stress-induced genotoxic damage can occur in a second cell type and on a molecular as well as chromosomal level. These results indicate that there may be a cellular genetic basis for some of the effects of stress.