The prevalence of tetracycline-resistant oral bacteria in healthy 4- and 6-year-old children who had not received antibiotics during the 3 months prior to sampling was investigated. Of the 47 children sampled, 46 harboured tetracycline-resistant bacteria. The median proportion of cultivable anaerobic and aerobic oral bacteria resistant to tetracycline was 1.1% and the MIC50 of these was 64 microg ml(-1). The majority (56%) of tetracycline-resistant bacteria were resistant to at least one other antibiotic, usually erythromycin. The most commonly identified tetracycline-resistant bacteria were the oral streptococci (65%), the next most prevalent groups were Veillonella spp. (10%) and Neisseria spp. (9%). The most frequently identified tetracycline resistance determinant was tet(M). The results of this study have shown that tetracycline-resistant oral bacteria were widespread amongst the children studied.