Volvulus of the large bowel is the third most common cause of colonic obstruction. A patient with colonic obstruction or delayed small intestinal transit may frequently have bacterial overgrowth and increased breath hydrogen (H(2)) and/or methane (CH(4)) excretion because the bacterium can contact with food residues for a longer time. A 39 year old woman attended our hospital with complaints of abdominal pain and distension. This patient's abdominal radiograph showed an inverted U-shaped shadow. The fasting breath CH(4) level was 26 ppm. An endoscopic procedure was immediately carried out with suspected sigmoid colon volvulus, and detorsion was achieved. There was resolution of the sigmoid volvulus after colonoscopy, and breath CH(4) concentration in the next morning decreased to 10 ppm. A liquid meal was supplied at noon on the second hospital day. The breath CH(4) concentration increased markedly to 38 ppm at 18:00 although she had no abdominal symptoms. This value peaked at 42 ppm at 18:00 on the third hospital day and was gradually reduced to 20 ppm the next day. The breath H(2) concentration value kept a low level during fasting and increased markedly to 51 ppm the next day after a liquid meal was supplied. The next morning, fasting breath H(2) concentration rapidly decreased to 6 ppm. This suggests that changes in breath H(2) levels may reflect transient malabsorption after a liquid test meal is supplied. In conclusion, breath H(2) and CH(4) analysis may be another tool for evaluating the intestinal circumstances.