Sister chromatid exchange (SCE) analyses were carried out in hospital nurses to determine whether an increased frequency of SCE may be used as an indicator of occupational exposure to potentially harmful antineoplastic drugs. In our study of 18 oncology nurses who handled these agents for an average of three days per week, we found no increase in mean SCE frequency (9.3 +/- 1.7 SCEs/cell) and no difference in the distribution of individual mean SCE frequencies compared to a group of 18 nurses who did not handle these drugs (9.5 +/- 1.5 SCEs/cell). There was a great deal of individual variation in mean SCE frequency as well as in SCE values in individual cells. No relationship with SCE frequency was found in terms of a subject's age, or the number of days of exposure to the drugs. Since conflicting results have been reported in persons handling antineoplastic drugs, SCE analysis alone is probably not a reliable indicator of exposure to possible mutagenic/carcinogenic effects of these drugs. SCE analysis may be helpful in conjunction with other studies, such as an analysis of urinary mutagens, or in studies of occupational exposure to agents other than antineoplastic drugs which may have a more noticeable effect on SCE frequency.