Parents and guardians of Japanese infants attending a dental clinic for their first routine dental examination were surveyed about their attitudes toward and understanding of the effects of ion drinks. The survey questioned the experiences resulting from administration, motives for use of the drinks, time of starting use of the drinks, and understanding of the relationship between the drinks and dental caries. In addition, the hydrogen ion concentration of various ion drinks commercially available on the Japanese market were measured in relationship to cariogenicity. Slightly more than 70% of the infants had been given ion drinks. The most frequent reason for using the drinks was because it had been recommended by the pediatrician followed by the belief that it was good for the health. Seventy-five percent of the infants were taking the drinks before 1 year of age. Ten percent of the infants were given the drinks in a nursing bottle, and 58% of the guardians answered that the drinks had no deleterious dental effects, indicating their poor understanding of the situation. Most of the drinks had a highly acid hydrogen ion concentration (below pH 4), indicative of extreme cariogenicity.