The serological properties of phospholipids were observed on the extraction of phospholid from the canine colon mucosa and the complement fixation test was done on the serum of patients in various disease. And the results were as follows. 1. The antigenicity of colon phospholipids antigen in vitro was a little high in comparison with that of the extracted antigen of colon mucosa by physiological salt solution, but the species specificity was not observed. 2. The positive cases of this reaction were 40 in 170 cases of various diseases and there were 22 cases with diseases of the digestive organ in them. Therefore, this reaction respectably had the specificity to diseases of the digestive organ. 3. The test of ulcerous colitis in diseases of digestive organ showed remarkable positive and the organic specificity of colon phospholipids was indicated. 4. No direct correlation between this reaction and the serological reaction of syphilis (Ogata's method) was not observed. 5. As for the correlation between this reaction and serum protein picture, the parallel correlation between this reaction and the increase of γ-globulin was considerably observed. 6. The correlation between the positive result of this reaction and the positivity of serum colloidal reaction was observed.