The effects of handling antineoplastic drugs were examined in 17 nurses working in a pneumology department in a hospital in the Paris area. Twenty-five others in the same department who were not handling such drugs acted as controls. Exposure to antineoplastic drugs was evaluated by questionnaire and by assessment of urine mutagenicity. The cytogenetic repercussions of exposure were assessed by examining sister chromatid exchanges and chromosomal abnormalities in circulating lymphocytes. The urine of the exposed nurses was significantly more mutagenic than that of the controls. No cytogenetic abnormalities were revealed in the exposed subjects since both these and the control nurses exhibited similar frequencies of chromosomal abnormalities and similar average numbers of sister chromatid exchanges in circulating lymphocytes. However, in smokers, the urine was significantly more mutagenic compared to that of nonsmokers, chromosomal abnormalities were twice as frequent, and the number of sister chromatid exchanges was significantly larger. Comparison of these results with the findings of other authors suggests that the moderate exposure to antineoplastic drugs prevailing in this pneumology department (i.e., an average of about 11 infusions per week) does not cause detectable cytogenetic abnormalities even though it significantly increases urine mutagenicity.