Campylobacter jejuni has become one of the most important causes of infectious diarrhea in the United States. We examined the utility of Gram's stain of stool for the rapid presumptive diagnosis of Campylobacter enteritis in a large, urban hospital and found that this test has a sensitivity of 43.5% and a specificity of 99.4%. We believe that Gram's stain of stool could be used to direct the early management of up to one half of patients infected with this pathogen.