The present invention provides an antihuman TNF-.alpha. antibody activity lowering inhibitor comprising a protein source(s) and/or carbohydrate source(s), in the treatment of inflammatory bowel syndrome with repeated administration of anti-TNF-.alpha. antibody; and a kit preparation wherein a freeze-dried antihuman TNF-.alpha. antibody and the activity lowering inhibitor in the above repeated administration of the anti-TNF-.alpha. antibody are separately contained in a plastic container so that they can communicate with each other. According to the present invention, in the drug therapy to the patients with inflammatory bowel syndrome, therapeutic agents which inhibit the inflammation for long periods without accompanying serious side effects can be provided.