The difference of the effect of cornins extracted from various kinds of living tissues was examined by employing several cell lines in vitro. And the inhibitory effect on tumor growth of the cornins was tested on the mice transplanted with Ehrlich ascites carcinoma. The results are as follows: 1) The antimitotic effect of canine intestine cornin (CIC) was more effective on Ehrlich ascites carcinoma cells in vitro (JTC-11) than that of bovine intestine cornin (BIC) and that of porcine intestine cornin (PIC). 2) Dialysable fraction, undialysable fraction and crude of CIC showed similar activities on the JTC-11 cell line. 3) The antigenicity of CIC was not proved by the hemagglutination test and no mice injected intraperitoneally with large doses of CIC showed any intoxication and disturbance. 4) The inhibitory effect of CIC on tumor growth was the strongest in the three kinds of the intestine cornins with Ehrlich ascites carcinoma and some of tumor-bearing mice were cured completly by the intraperitoneal injections of CIC. 5) The cornin extracted from liver of normal rats (RLC) had marked inhibitory effect on the cell growth of the short-term cultured cell line (RLM-1) and the long-term cultured cell line (RLN-10) originated from normal rat liver, but no effect was observed on the cell line in culture which came from the DAB ascites hepatoma of the same line rat.