PROBLEM TO BE SOLVED : To provide methods, systems and devices for treating diseases of the gastrointestinal tract using ablative energy. SOLUTION : Methods, systems and devices are described for treating diseases of the gastrointestinal tract, including ulcerative colitis, by delivering ablative energy to a tissue surface of the gastrointestinal tract and ablating the tissue to a controlled depth. Ablating the tissue may include removing a biofilm layer or coagulating tissue. The techniques may be applied to treat ulcerative colitis, ulcerative proctitis, colitis, irritable bowel disease, Crohn' s disease, or dysplastic lesions. SELECTED DRAWING : Figure 3A COPYRIGHT : (C)2019, JPO&INPIT