We tested the hypothesis that children with chronic relapsing colitis induced by Clostridium difficile toxin have defective antibody responses to C. difficile toxins as a cause of their underlying illness. Six such children were tested for serum IgG and IgA antibody to C. difficile toxin A. These six children had lower IgG anti-toxin A levels than 24 healthy children (p = 0.026) and 18 healthy adults (p = 0.0008). Five patients treated with 400 mg intravenously administered gamma-globulin per kilogram every 3 weeks had significant increases in IgG (p = 0.01) but not IgA anti-toxin A (p = 0.406) levels, and all five had clinical resolution of their gastrointestinal symptoms as well as clearing of C. difficile cytotoxin B from their stools. These observations suggest that a deficiency of IgG anti-toxin A may predispose children to the development of chronic relapsing C. difficile-induced colitis. In such cases, intravenous gamma-globulin therapy may be effective in producing clinical remission.