The purpose of this study was to evaluate the influence of caffeine and theophylline on the development of dental caries in rats. Six Wistar dams (spf), mutans streptococci free, were obtained, each with six male pups. The dams were infected by Streptococcus sobrinus 6715 and divided into three groups which received during the lactating period: (1) diet 2000; (2) diet 2000 plus caffeine (2 mg/100 g) and (3) diet 2000 plus theophylline (0.57 mg/100 g). After weaning, the pups were infected by S. sobrinus, placed in a König-Höfer programmed feeder machine, and received 17 meals daily at hourly intervals, for five weeks. During this time the pups were fed with the same diet that their dams were. The percentage of S. sobrinus relative to total flora was significantly higher in the theophylline group. The results for slight (Ds) and moderate (Dm) dentine lesions, for smooth-surface and sulcal scores were statistically higher for the theophylline group than the other groups. Salivary assays did not demonstrate significant inorganic alterations in salivary composition. Caffeine and theophylline groups showed the highest ulcer score. It is concluded that caffeine does not affect the cariogenic potential of the diet, however theophylline can increase the development of dental caries, and this effect may be related to organic alterations of salivary composition.