Acute gastroenteritis is a potential cause of substantial morbidity in U.S. military personnel during deployment. This study was conducted to evaluate enteric pathogens associated with diarrhea in a U.S. military population on deployment in Cairo, Egypt, during November 1993. Enteric pathogens found to be associated with cases of diarrhea included: enterotoxigenic Escherichia coli (ETEC), 27% (22% heat-stable [ST], 3% heat-labile [LT], and 2% ST/LT producers); Campylobacter spp., 3%; and Salmonella spp. 3%. Other enteric pathogens, namely Shigella, Aeromonas, Plesiomonas, Vibrio spp., Bacillus cereus, and enteric parasites, were not found in any of the 36 patients. Of the 8 patients who were ETEC-positive, three expressed colonization factor antigens (CFA)/II, and two expressed putative colonization factor antigen (PCF) 0159. All of the latter isolates produced ST. ETEC with different surface protein antigens were found to have surface hydrophobicity in the range of 0.2 M to greater than 2.0 M. Plasmid profiles of the ETEC strains showed no correlation with toxin production. In vitro susceptibility testing of the ETEC strain showed that 32% of the strains were resistant to three or more antimicrobial agents, whereas 24% showed 100% susceptibility. The enteropathogens tested were susceptible to norfloxacin, ciprofloxacin, and nalidixic acid, suggesting that the quinolones might be useful for the treatment of diarrheic patients.