A 53-year-old woman suffered six episodes of Clostridium difficile-pseudomembranous colitis. The serological follow-up demonstrated the absence of a rise in IgG and IgA to toxin A. Human pooled gamma globulin was administered during the fifth relapse and raised IgG levels to toxin A. Normal stools reappeared a week later. The role of the antibodies to toxin A and gamma globulin in C. difficile colitis are discussed.