Eighteen different infants' drinks from five manufacturers were examined for their carbohydrate, calcium, phosphorus and acid contents, and their attack on tooth mineral. Seven of the drinks were compared with nine varieties of adults' soft drinks, and demineralization was studied with and without the presence of a cariogenic oral streptococcus. The influence of the acids already in the drinks in dissolving Ca and P outstripped that of any acid generated in these studies in vitro by microbial fermentation of the sugars they contained, giving an indication of their relative erosiveness rather than their cariogenic action. Various other features of the drinks relevant to dental health were identified. Titratable acid was a better guide than pH to their dental properties. Although there were considerable differences between the various infants' drinks taken as a group, their acidity levels and demineralizing powers were generally lower than those of the adults' drinks.