Antigenicity of ribosomal digest of Ehrlich ascites tumor was studied in vivo. Antitumor activity was observed by intraperitoneal transplantation of Ehrlich ascites cells, comparing with body weight between control group and immunized ones, which were treated with tumor ribosomal digest. The body weight increasing curve in case of 100～500×10(4) Ehrlich ascites cells inoculum was no visible differences between control group and immunized ones. The antitumor effect was visible inc ase of 50×10(4) tumor cells inoculum, the LD50 of immunized group was 16 days and that of ontrol 14 days. The effect was more clearly observed
in case of 10×10(4) tumor cells inoculum. The LD50 of immunized group was 17 days and that of control 14 days. No visible effect were in mice transplanted with Ehrlich ascites cells on the back between control and immunized group. Neutralization experiment with rabbit anti-serum prepared by Ehrlich ascites tumor ribosomal digest was observed by multiple dilution method. The effect was most strong at 0.2ml of anti-serum for 50×10(4) tumor cells.