Plaque fluid and saliva were collected from 4 irradiated monkeys (Macaca mulatta) and from 8 groups of non-irradiated controls all of which were receiving a cariogenic diet. Plaque was also collected from a non-irradiated group which was fed a non-cariogenic diet. The investigation will provide information on the biochemical composition of plaque fluid and saliva associated with the development of caries and provide enhanced insight into the pathogenesis of dental caries. Composition of the plaque fluid was influenced by ingestion of sucrose.