In this study the efficacy of a topic intestinal antibiotic, Rifaximine, on quiescent ulcerative colitis has been evaluated. Twelve patients, aged 20-45 years, affected by ulcerative colitis, with an endoscopic evidence of remission and abdominal symptoms referable to microflora alteration have been admitted. All patients have been treated with Rifaximine 800 mg p.o. three times a day for 10 consecutive days. Meteorism, abdominal pain, and the stool number have been evaluated at admission and on the 2nd, 4th, 6th, 8th and 10th days of therapy. All symptoms and clinical parameters showed a mean significant early reduction on Rifaximine treatment. Only one patient failed to show a substantial improvement. In no case side effects appeared.