Campylobacter fetus ss. jejuni has been recently recognized as a common human enteric pathogen; however, the pathology and pathophysiology of the enteritis caused by this agent are still largely obscure. We report 4 patients who presented with acute abdominal pain and bloody diarrhea and who had C. fetus ss. jejuni isolated from fecal cultures. Each patient showed a fourfold rise in serum IgG titer to the organism isolated. In all 4 patients colonic involvement was noted on sigmoidoscopic examination. Biopsy specimens showed acute colitis with inflammatory infiltrates of the lamina propria and crypt abscesses. Clinical improvement was complete in all patients after therapy with erythromycin. These results suggest that clinicians should consider Campylobacter enteritis in the differential diagnois of acute colitis.