Long-term, low levels of antineoplastic drugs and ionizing radiation in the work environment may have genotoxic effects on chromosomes in personnel. The effects of ionizing radiation is acknowledged in occupational medicine and therefore various measures have been undertaken to prevent such effects. However, there are no protective measures for workers exposed to antineoplastic drugs. In this study metaphase chromosome preparations were analyzed in 126 nurses and radiology technicians. They were divided into three equal groups. The first group consisted of shift nurses in an oncology department handling antineoplastic drugs. The second group consisted of radiology technicians in a radiology department and the third group acted as controls. Structural chromosomal aberrations were increased among those nurses exposed to antineoplastic drugs in comparison with technicians (P less than 0.05) and controls (P less than 0.01), respectively.