OBJECTIVE: To study the distribution of antibiotic resistant Escherichia coli in the fecal flora of healthy children in Greece. METHODS: Rectal swabs were collected from 181 children, not suffering from infections and not undergoing antibiotic treatment, aged 6 months to 6 years, outpatients of a pediatric hospital, and plated on McConkey agar with ampicillin or trimethoprim. Isolated resistant colonies were identified to the species level and E. coli strains were studied further by molecular methods. RESULTS: Forty-four per cent of the children carried resistant E. coli, and in 20% resistance was transferable. Forty-seven per cent of the children with no history of antibiotic consumption during the last year were found to carry resistant strains in their feces, and transferable R plasmids were present in 23% of them. Forty per cent of the strains and 30% of the transconjugants were multiresistant. Although plasmids of various molecular weights and restriction endonuclease digest patterns were identified, six 60-MDa and four 80-MDa plasmids, originating from epidemiologically unrelated children, were found to be similar. CONCLUSION: Normal flora E. coli in Greece seems to constitute an important reservoir of resistance genes. Eradication of resistance from a population that comes into frequent contact with antibiotics seems to be difficult.