Thirty patients on hemodialysis were randomized to receive either Probinul neutro® or placebo for four weeks. Total plasma p-cresol concentrations was assessed at baseline, and 15 and 30 days after treatment start. At the same study times, ease and frequency of defecation, upper and lower abdominal pain, stool shape, borborygmi and flatus were quantified by subjective assessment questionnaires.