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The effects of Corynebacterium parvum on the Lewis rung tumour and its metastases have been studied. Intravenous but not intraperitoneal or subcutaneous C. parvum reduced the growth of the primary tumour. Both intravenous and intraperitoneal C . paruum significantly reduced pulmonary metastases. When combined with excision of the p r i m r y tumour, C . parvumgiven not more than 2 days before excision caused only slight reduction of metastases, but when given intravenously or intraperitoneully 3-4 duys before excision, metastases were signiJicantly reduced and some mice were cured of tumour. Subcutaneous C. paruum had no effects on metastases. Non-specific operation (amputation) increased tumour metastases, but C. parvum counteracted this. Metastases were significantly increased by the administration of silica and cortisone acetate but were umffected by trypan blue. The antimetastatic action of C. paruum was not significantly altered by these treatments. Thymectomy and irradiation did not afect tumour metastases or the antimetastatic action of C. parvum, whereas antilymphocyte serum depressed metastasis and abrogated the protective effects of C. parvum.It appears that the inhibitory effects of C. parvum on tumour metastases are mediated through macrophages in concert with a subpopulation of Tz lymphocytes.

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