Twenty-six infants and young children with acute dehydrating diarrhea associated with Campylobacter jejuni participated in a randomized, double-blind, placebo-controlled therapeutic trial. Of 25 patients who completed the study, 11 were treated for five days with oral erythromycin ethylsuccinate (40 mg/kg/day in divided doses), and the rest received matched placebo. Although erythromycin significantly shortened the duration of C jejuni excretion, it appeared to exert no effect on the clinical course of the illness. This failure may be explained on the grounds that most patients' symptoms were resolving spontaneously when they were admitted to the trial. However, as all but eight children were infected with at least one erythromycin-resistant enteropathogen in addition to C jejuni, the clinical failure of antibiotic therapy may have been due to erythromycin's inability to eliminate these organisms.