Getting a hint from immunologic specificity of bacterial polysaccharide, the author, with Julianelle's method modified by Hosoya, isolated the polysaccharide-like substance from cellabundant and actively proliferous cancerous tissue, and applying it as antigen to patient serum in the precipitation reaction, got the following good results in diagnosis of cancer and other malignant tumors. 1) Obtained diagnosis rates are as follows: the positive results in case of patients with cancer, sarcoma and other malignant tumors ……88%; the negative results in case of patients of benign lesions ……85.1%; the average hitting rate in total cases ……86.5%. However, the differential diagnosis between cancer and sarcoma is impossible. 2) Cancerous tissue appl...