The aim of the study was to investigate those factors that could be correlated with mutans streptococci (MS) transmission and caries decay (dmft) among children aged 30 months; 85 boys and 70 girls were included. A questionnaire concerning the nutrition history and childhood nursing practice was completed by the parents. The caries status of the children was examined, and the salivary MS of the children as well as their mothers (n = 155 pairs) were determined by Dentocult® SM. Two isolates were picked from spatulas from 34 mother-infant-pairs. The pure cultures (n=128) were identified by biochemical tests and by their membrane fatty acid profile (MIDI, Newark USA). Bacteriocine-fingerprinting was performed for all isolates to determine the similarity within each family and among the strains. 65% of the mothers and 24% of the children harboured high salivary MS (scores SM 2 and 3). Furthermore, higher counts could be estimated in 50% of the mothers and in 9% of the children.59% of the strains were bacteriocinogen against S. sanguis, S. oralis, S. gordonii, S. mitis and S. salivarius. 41% of mother-infant-pairs harboured the active strains and, furthermore, half of them harboured identical strains. The caries decay of the children was registered at a mean dmft of 0.6 ± 2.0. Higher scores of MS correlated significantly with higher caries decay (Spearman's correlation coefficient 0,32712, X2-test p 0.0001). The upper incisors showed significantly more frequent decay (X2-test p 0.001). Furthermore, a positive correlation could be found between high MS counts in children and bottle-feeding at night (X2-test p 0.003). The data suggest that bottle-feeding, especially at night, may support the fidelity of MS transmission from mothers to infants and that bottle-feeding at night may contribute to a higher caries rate. Palabras clave: caries prevention, early childhood caries, behaviour of mothers, bottle-feeding, mutans streptococci, bacteriocin-fingerprinting, transmission