Abstract  In vivo cytogenetic effects of cyclophosphamide was simultaneously evaluated in 7 mouse organs. Cyclophosphamide produced most pronounced changes in the urinary bladder and bone marrow, the main target organs for this carcinogen. Mutagenic effects of the preparation were also detected in the lungs, large intestine, and stomach. This approach can be used for evaluation of organ specificity of mutagens and for prediction of the carcinogenic effects of chemical compounds.