To determine the value of direct dark-field microscopy for diagnosing enteritis due to Campylobacter fetus subsp. jejuni, we examined 1,377 human fecal specimens for bacteria with typical Campylobacter darting motility, leukocytes, and erythrocytes. Eighty-four specimens (6.1%) grew C.fetus subsp. jejuni. Of the 48 specimens showing Campylobacter motility, 30 (62%) grew C. fetus subsp. jejuni. The sensitivity, specificity, and predictive value of observing Campylobacter motility were 36%, 99%, and 62%, respectively. The predictive value of detecting Campylobacter motility was improved if the specimens were diarrheal (23 of 31, 74%), leukocytes were present (25 of 33, 76%), erythrocytes were present (22 of 27, 81%), or if all of the above findings were present (18 of 20, 90%). The sensitivity of detecting Campylobacter darting motility was highest if specimens were examined within 2 h of arrival in the laboratory (15 of 30, 50%) as opposed to after 2 h (15 of 53, 28%; P less than 0.01). Prompt dark-field microscopic examination of diarrheal stool specimens is valuable for the presumptive diagnosis of Campylobacter enteritis.