Ten cases of antibiotic-associated pseudomembranous colitis in children are reviewed. The ages ranged from 4 years to 17 years; the most frequently implicated antimicrobial agents were penicillins in six children and clindamycin in two. Stool assays showed specimens from all ten patients yielded a cytopathic toxin which was neutralized by Clostridium sordellii antitoxin with titers ranging from 1:40 to 1:40,000. Bacterial cultures of nine specimens uniformly yielded Clostridium difficile with a median concentration of 10(5.4) organisms per gram of wet weight. All nine isolates of C difficile showed a vitro production of a cytopathic toxin which was similar to or identical with that which was detected in the original stool specimen. All ten patients recovered. Six were treated with oral vancomycin and showed a good therapeutic response; one patient, however, suffered two relapses when treatment was discontinued, requiring a total of three courses of oral vancomycin. Two patients received cholestyramine and responded well. These observations provide supportive evidence that C difficile is responsible for antibiotic-associated pseudomembranous colitis in children and document efficacy of the newer therapeutic modalities in this patient population as well.