The authors studied the metastasis-inhibiting effect of various dosages of tiazofurin in mice inoculated with a low (LLT) and a highly (LLT-HH) metastatic variant of the Lewis lung carcinoma. The tumor cells were inoculated intravenously (lung colony assay), intramuscularly (muscle-lung metastasis model), and intrasplenically (spleen-liver metastasis model), respectively. In the lung colony assay the tiazofurin proved to be curative. In the muscle-lung and the spleen-liver model the tiazofurin treatment, started after the removal of the parent tumor, drastically decreased the number of metastases in both model systems and brought about a significant prolongation of the survival time in the spleen-liver model. Authors suggest that tiazofurin as one of the most promising candidates for metastasis prevention and inhibition in human beings, too.