A case study is presented of a 47-year old, white female with a 1-year progressive history of diarrhea up to 20 liquid stools per day, accompanied by an 18-pound weight loss. She had presented with previous workup of gastroscopy revealing two stomach ulcers; colonoscopy revealing nonspecific colitis and one polyp that was subsequently removed and found to be benign; and a negative abdominal ultrasound. She was Helicobacter pylori negative and HIV negative. Her stools had been negative for blood, ova and parasites, and culture. She had been using well water from a new well for 2 years. String test was negative for Giardia She had no diarrhea during a day of fasting. Carbon 14 D-xy-lose breath test was positive. She was discharged on a 14-day course of 500 mg. Augmentin (amoxicillin 500 mg. with clavulanate potassium 125 mg.) by mouth every 8 hours. Seven weeks later, she was having four to five formed stools per day and had gained 16 pounds.