Disclosed is rifaximin polymorph form h, wherein the polymorph exhibits an X-ray powder diffraction pattern having characteristic peaks expressed in degrees 2q (+/- 0.20 degree q) at 5.3, 6.1, and 7.9 or 5.3, 6.1, and 12.7 or 5.3, 6.1, and 8.8. Further disclosed is a pharmaceutical composition which comprises the polymorph Form h as defined above and one or more pharmaceutically acceptable excipients for use in treating, preventing or alleviating a bowel related disorder such as irritable bowel syndrome, diarrhea, microbe associated diarrhea, Clostridium difficile associated diarrhea, travelers diarrhea, small intestinal bacterial overgrowth, Crohns disease, chronic pancreatitis, pancreatic insufficiency, enteritis, colitis, hepatic encephalopathy, and pouchitis.
