Probiotics are dietary supplements claiming to have prophylactic and therapeutic properties against different diseases. Products of this kind contain beneficial micro-organisms with the ability to stimulate health promoting bacteria and inhibit pathogens. The most common probiotics are fermented milk products, best known probiotic bacteria are lactobacilli and the most common application is gastrointestinal disease. Several researchers claim that prolonged oral supply of probiotics also may have inhibitory effect on the development of dental caries and on periodontal pathology by competition with patogens for adhesion and nutritional factors. It is also claimed that microbial influence of this kind increase beneficial immune response and diminish periodontal inflammation. Animal and clinical experimental evidence supports these views. However, the clinical investigations are often of short-time nature, with low number of participants and with modest differences between probiotic groups and the placebos. Recent research reports and reviews indicate that the interest for oral probiotic questions is considerable. However, practical and ethical considerations are obstacles for large scale clinical trials. At present the prevalent view is that probiotics may be a supplement to personal and professional dental prophylaxis but there is no basis to recommend such measures to dental patients.