In 37 children with Campylobacter enteritis seen over a 6-month period, ages ranged from 2 weeks to 15 years. The sex ratio (male:female) was three:two. Fever, diarrhea, and bloody stools occurred in about 90% of patients. Blood appeared in the stools characteristically 2 to 4 days after onset of symptoms. Over 90% of older children developed abdominal pain. Vomiting was mild and occurred in 30% of patients. Dehydration was not a feature. Infection occurred in all social classes and was not associated with parental occupation, travel, or animal contact. The illness often presented characteristically and a rapid laboratory diagnosis could be made in patients presenting acutely by direct phase-contrast microscopy of stools. The organism persisted in the stools for up to seven weeks in untreated patients, but could no longer be cultured after 48 hours of therapy with erythromycin, to which all strains were highly sensitive. Significant serologic responses were elicited using a serum bactericidal assay. The Skirrow-type selective medium used by us could be improved by increasing the concentration of polymyxin B sulfate to 5 microgram/ml.