Purposes: (a) To measure the urinary excretion of antineoplastic drugs of three patients during 48 h after the administration of cyclophosphamide (two patients) and 5-fluorouracil (one patient). (b) To evaluate environmental contamination with antineoplastic drugs via excreta of patients in the home setting. (c) To evaluate exposure of family members to antineoplastic drugs by measuring the drugs in their urine during the 48 h after completion of the chemotherapy by the patients. Methods: Two patients were administered cyclophosphamide by i.v. bolus injection. One patient was administered 5-fluorouracil by i.v. bolus injection and thereafter immediately administered the same drug by continuous infusion for 46 h. Urine samples from the patients administered cyclophosphamide and their family members, and wipe samples from their home environment, were analysed for the unchanged form of cyclophosphamide. For 5-fluorouracil, the urine samples from the patient and the family member were analysed for the 5-fluorouracil metabolite α-fluoro-β-alanine. Wipe samples were analysed for 5-fluorouracil. Drugs were detected and quantified with gas chromatography in tandem with mass spectroscopy-mass spectroscopy or by high-performance liquid chromatography with ultraviolet-light detection. Results: A total of 35 and 16 urine samples were collected from the three patients and their family members, respectively. The drugs were detected in all samples. Cyclophosphamide was detected at levels of 0.03–7.34 ng/cm2 in 8 of the 12 wipe samples obtained from the homes of the patients administered cyclophosphamide. For the patient administered 5-fluorouracil, drug levels in his home environment were below the limit of detection. Conclusion: We demonstrated contamination of the home setting and exposure of family members to cyclophosphamide via the excreta of outpatient receiving chemotherapy. Exposure of the family member of the patient administered 5-fluorouracil was also demonstrated. These findings indicate the importance of strict precautions by the members of treated cancer patients as well as healthcare workers, to reduce the risk of exposure to antineoplastic drugs.