Effect for the host and the tumor of the streptococcal preparation, OK-432, and Bacillus Calmette Guerin (B.C.G.) were comparatively studied. Its results are described below: 1) Granulomatous hepatitis with giant cells was observed in 4 of 5 mice (80%) receiving 5×10(7) B.C.G. organisms by i.p. injection. But there are no pathological findings in liver receiving the same bacterial counts of OK-432 as those of B.C.G.. 2) Neutrophilia in mice receiving 4×10(5) B.C.G. organisms i.p. is more remarkable than in mice receiving i.p. OK-432 containing 5×10(7) streptococcal hemolyticus. 3) By administrating OK-432 or B.C.G. i.p. at the same quantity mentioned above, peritoneal cells, particularly macrophages and neutrophils, are exudated more markedly in mice receiving OK-432 than B.C.G.. 4) At the same dosage, the survival rate of the C3H mice pretreated i.p. with OK-432 was more prolonged than the rate of the C3H mice pretreated i.p. inoculation of methylcholanthrene-induced sarcoma. The results stated above lead to the conclusions that B.C.G. has a liver damage, i.e., granulomatous hepatitis as the side effect by administrating the massive dose in contrast to OK-432. B.C.G. is stronger than OK-432 as the general stimulant to the host, and OK-432 is stronger than B.C.G. as the local stimulant. And consequently the host-mediated antitumor action of OK-432 is more predominant than B.C.G. at the dose that the author investigated in this paper.