It is well established that the intestine is an important site responsible for the local immune system. It is speculated that people suffering from constipation and carrying fecal residues in the intestine may have a decreased function of this immune system. In this study, colon irrigation, which is cleansing of the colon using a simple hydrotherapy instrument, was performed in 10 subjects with or without the disease. The number of leukocytes and their demarcation were then evaluated. The number and ratio of lymphocytes increased significantly after irrigation. This result suggested that colon irrigation might induce lymphocyte transmigration from gut-associated lymphatic tissues into the circulation, which may improve colon and immune system function.