An agent for improving a function of detecting lesion in the digestive tract by CT colonography or MR colonography characterized by containing a serotonin 5-HT4 receptor stimulant as the active ingredient and a composition for washing the intestinal tract by CT colonography or MR colonography characterized by containing a colloid osmotic pressure controlling agent and/or a crystalloid osmotic pressure controlling agent as the active ingredient(s). Thus, it is possible to provide a method of reducing an area in which examination cannot be conducted (i.e., a lesion-undetectable area) due to the remaining intestine-washing water or pooled intestinal fluid frequently observed in the large intestinal tract after washing in an examination of colon cancer, etc. by CT colonography or MR colonography. It is also possible to provide a method of elevating the subjects acceptability for CT colonography or MR colonography.
