objectives: to establish a relationship between dental caries with the degree of streptococcus mutans present in the salivary flow and saliva buffer ability in 111 healthy adolescents seen at the pediatrics outpatient clinic of the hospital das clínicas de pernambuco. methods: intraoral examinations were performed and dental records filled to determine dmfs-s (decayed, missing teeth and filled permanent dental surfaces). following, saliva was collected to determined salivary flow and buffer ability. front teeth were scrapped to quantify streptococcus mutans present in the bacterial plaque. results: the population assessed had predominantly low caries activities with buffer ability of normal saliva and deficiency of salivary flow. the numbers of s mutans in the bacterial plaque exceeded 105 cfu/mg in the majority of individuals in the population studied. conclusions: caries activity was inversely proportional to the buffer capacity and directly proportional to the presence of streptococus mutans in the bacterial plaque. this low carie activity could be derived from the daily tooth-brushing with fluor dentifrices.