The Leuko-Test yielded a negative predictive value of 98.4% when it was used to screen 325 patients for inflammatory bacterial enteritis and a negative predictive value of 99.4% when it was used to screen 416 stool specimens for those from which enteric pathogens would likely be recovered when cultured. Neither microscopy for fecal leukocytes nor an assay for fecal occult blood, alone or in combination, allowed for the reliable detection of invasive bacterial enteritis or the reliable selection of specimens for culture. When positive in the Leuko-Test, specimens collected from patients after the third day of hospitalization did not yield enteric pathogens when the specimens were cultured, and specimens collected from inpatients within the first 3 days of hospitalization or from outpatients did not contain Clostridium difficile toxin A. As a screening test, the Leuko-Test has the ability to generate rapidly a result which can support the presumptive diagnosis of inflammatory bacterial enteritis or which can be used to determine the suitability of stool specimens for bacteriologic culture.