Five well-characterized foods were used to compare two systems for estimating the cariogenic potential of food: human plaque-acidity using interdental metallic touch electrodes, and cariogenicity testing in rats. Both systems identified the same food as the least cariogenic or acidogenic food and identified the same three foods as being both cariogenic in rats and acidogenic in man, although the ranking of these foods differed. The systems differed in their assessment of potato chips, a food high in cooked starch and low in free sugars. The results confirmed that non-acidogenic foods are non-cariogenic, but that foods acidogenic in man may exhibit a greater range of cariogenicity in rats. Data from both human plaque pH studies and rat caries models may permit better assessment of cariogenic potential of foods containing fermentable carbohydrates.