Pasteurella ureae is uncommonly isolated from patients and rarely causes disease. The case of a patient with spontaneous bacterial peritonitis caused by P. ureae is described and contrasted with other reported cases of P. ureae colonization and infection. Respiratory colonization has been described in older patients, predominantly men, with underlying lung disease consisting principally of bronchitis, bronchiectasis, and tumors. Only 11 patients (including the present patient) have been reported to have illness with P. ureae. Seven had meningitis, two had pneumonia, and one had hepatitis. Skull fracture, alcoholism, and liver disease are common antecedents of P. ureae infection.