Bacterial diarrhea can be classified into two clinical entities, noninflammatory diarrhea and inflammatory diarrhea syndromes. The latter type of diarrhea is characterized by bloody and puruloid mucus stool, and is often accompanied by fever, tenesmus, and severe abdominal pain. Pathogenic bacteria causing the inflammatory diarrhea syndrome include Salmonella, Vibrio, Shigella, enteroinvasive and enterohemorrhagic Escherichia coli, Campylobacter, Yersinia, Chlamydia, and Clostridium difficile. The pathologic changes in the inflammatory diarrhea syndrome range from a superficial exudative enterocolitis to a transmural enterocolitis with overt ulceration. This syndrome is also designated as bacterial hemorrhagic enterocolitis because of its usual manifestation by bloody diarrhea. The diagnostic approach needs information on the patient's age, travel history, epidemiological associations, sexual practice, and medical history, including usage of antibiotics. Bacterial information can be obtained by microscopic study, culture, and the identification of specific bacterial toxins. Flexible colonoscopy with biopsy is useful for the differentiation of bacterial hemorrhagic enterocolitis from idiopathic ulcerative colitis and ischemic colitis. Physicians should be familiar with the diagnostic modalities used to detect the specific pathogens causing hemorrhagic bacterial enterocolitis; namely, bacterial culture, serology, histology, and nucleic acid technologies.