) This study proposes research on the exposure of health care workers to the drug cyclophosphamide, which is a human carcinogen and which is used extensively in cancer chemotherapy. Nurses and pharmacists who handle or administer antineoplastic drugs have been shown to have detectable amounts in urine at the end of the work shift, despite the use of biosafety hoods, gloves, and recommended work practices. Because end-of-shift urine measurements assess low level exposures only during the previous 1-3 days, and because spills and unplanned exposures occur sporadically, a method that assesses exposure over a longer period would be more useful in assessing effectiveness of work practices and other preventive measures. Hair analysis has been used extensively for detection of trace quantities of illicit drugs and some therapeutic drugs and current technology allows detection at the nanogram of drug/mg. of hair level. A method will be developed for assay of cyclophosphamide and a major metabolite, carboxyphosphamide, in hair. The method will be validated and a dose-response relationship established in rats. A pilot study of nurses and pharmacists who work with cyclophosphamide, and a control group, will then be done to assess exposure. Detection of the metabolite in human hair will distinguish internal absorption from external contamination from the work environment. If this pilot study is successful a larger study could be done of health care workers at various cancer treatment centers. In addition to assisting epidemiologic research, the proposed method would be a useful means of assessing and controlling exposure to antineoplastic drugs.