We examined how chemotherapy-induced myelotoxicity and the associated leukopaenia affect cancer metastasis in an animal model. Myelotoxicity was induced by a single injection of 5-fluorouracil (5-FU) or Cisplatin, administered to 7-week-old BALB/c mice. CT-26 murine colon carcinoma cells were injected into the lateral tail vein on days 0, 1, 3, 5, and 7 after anticancer drug injection. On day 14 after cancer cell injection, the number of pulmonary colonies was measured in a double-blind setting. Compared with Cisplatin, 5-FU induced severe leukopaenia and bone marrow suppression, while on day 5, both drugs induced severe myelotoxicity. The number of pulmonary colonies did not correlate with the severity of leukopaenia, regardless of the type or time of drug injection, except in the group pretreated with Cisplatin (3 days prior to cancer cell injection). Our results suggest that chemotherapy-induced myelotoxicity does not increase the incidence of cancer metastasis in this animal model.