The present invention relates to a method for the semi-quantitative determination of cariogenic bacteria in a sample of saliva and/or plaque, in which the microorganisms contained in a sample of plaque or saliva are brought into contact with a carbon source that is fermented to acid by the cariogenic bacteria. The microorganisms are then incubated under conditions which make possible selective acid formation by the cariogenic bacteria. The acid formation is then detected by determining the pH at least once within a period of 12 hours after adding the carbon source, wherein the cariogenic bacteria are determined semi-quantitatively in the sample by comparison of the pH with at least one reference value. In addition, the invention provides kits for carrying out such methods.