The invention provides a method for the treatment or prevention of microbial overgrowth in at least part of the intestinal tract of a subject, said method comprising administering an effective amount of an alginate oligomer to a subject in need thereof. Also provided is an alginate oligomer for use in the treatment or prevention of microbial overgrowth in at least part of the intestinal tract of a subject and a product containing an alginate oligomer and further pharmaceutical for the treatment of intestinal microbial overgrowth and/or a CFTR modulator as a combined preparation for separate, simultaneous or sequential use in the treatment or prevention of microbial overgrowth in at least part of the intestinal tract of a subject.
