A method of treating bowel diseases includes introducing a fluid into a portion of a patient's colon and applying energy thereto from an external energy source such that the fluid and the energy cooperate to treat tissue of the portion of the patient's colon in contact with the fluid. Another method of treating inflammatory bowel diseases includes sealing a portion of a patient's colon, introducing an electrically-conductive fluid thereto, and energizing an electrode disposed therein to treat tissue of the portion of the patient's colon in contact with the electrically-conductive fluid. Another method of treating inflammatory bowel diseases includes sealing a portion of a patient's colon and introducing a heated fluid at a temperature equal to or above 60° C. to treat tissue of the portion of the patient's colon in contact with the heated fluid.