Forphenicinol, S-2-(3-hydroxy-4-hydroxymethylphenyl)glycine, prolonged the survival period of mice implanted with Meth A fibrosarcoma or Lewis lung carcinoma. The effect was observed in the mice when the primary tumor was removed by amputation. At autopsy, metastasized tumors were found in all dead mice but no tumor foci were detected in any of the mice still alive at the time of sacrifice. Moreover, forphenicinol suppressed the growth of subcutaneously implanted adenocarcinoma 755. When combined with surgical resection of primary tumors, forphenicinol administration both before and after resection suppressed the growth of recurrent tumors and prolonged the survival period of the mice.