The effects of handling antineoplastic drugs were examined in a group of 23 nurses working in the hematology and oncology departments of different university hospitals in Ankara and in a group of 50 unexposed controls. The cytogenetic repercussions of exposure were assessed by examining sister chromatid exchanges (SCEs) in circulating lymphocytes which result from the breakage and rejoining of DNA at apparently homologous sites on the 2 chromatids of a single chromosome. A significant increased frequency of SCE is observed in nurses in daily contact with antineoplastics (n = 23, mean SCEs/cell +/- SE 6.5 +/- 0.2) as compared to a group of controls (n = 50, mean SCEs/cell 5.2 +/- 0.2). The nurses who smoked also had a higher SCE frequency (n = 15, mean SCEs/cell 7.0 +/- 0.3) than non-smokers, (n = 8, mean SCEs/cell 5.5 +/- 0.3). A significant increase (P < 0.001) in the mean number of SCE was found for non-smoking nurses as compared to non-smoking controls (n = 27, mean SCEs/cell 4.1 +/- 0.2).