Children with diarrhea admitted to a rehydration ward of a children's hospital in Bangkok were investigated to determine the prevalence of enteric pathogens, the extent of children's previous antibiotic therapy, and the frequency of plasmid-mediated antibiotic resistance among infecting bacteria. Rotavirus (36%), enterotoxigenic Escherichia coli (18%), Shigella (9%), Salmonella (6%), Campylobacter jejuni/coli (4%), and Vibrio cholerae (2%) infections were among 105 children with diarrhea. Antibiotics were detected in 29% of urines collected from children on admission. All Shigella, 83% of enterotoxigenic E. coli, and 40% of Salmonella were resistant to more than one antibiotic. Sixty-two percent of 24 antibiotic-resistant enteric pathogens transferred R factors to E. coli K12 by conjugation. Four of four multiresistant E. coli that produced heat-labile and heat-stable toxin transferred resistance and the ability to produce heat-labile toxin. An analysis of plasmids by agarose gel electrophoresis indicated enterotoxigenicity and antibiotic resistance were associated with separate plasmids in transconjugants from these six matings. Antibiotics are used frequently in the treatment of pediatric diarrhea in Bangkok, which has undoubtedly contributed to the high frequency of plasmid-mediated resistance among enteric pathogens.