Seven patients treated with oral cholestyramine for antibiotic-associated pseudomembranous colitis are reported. Response was variable with only one patient having a totally satisfactory clinical outcome. Five of seven patients had continued systemic signs with fever and ieukocytosis throughout the course of cholestyramine. Two observations were relatively consistent. First, six of the seven patients had a decrease in the number of daily stools during therapy. Second, all patients showed persistence of the cytopathic toxin in stools obtained after three to seven days of cholestyramine therapy. Six patients who were subsequently treated with oral vancomycin had a prompt clinical improvement and clearance of the cytopathic toxin in the stool.