The aim of this study was to evaluate in vivo whether short-term consumption of commercial yogurt modifies the levels of salivary mutans streptococci and lactobacilli in young subjects. A total of 84 volunteers were selected and divided into two groups (test and control). Subjects from the test group were asked to eat a pot of commercial yogurt twice a day for 2 weeks. No dietary restrictions, except a prohibition on eating yogurt and other fermented dairy products, were required to the subjects from the control group. The salivary colonisation of mutans streptococci and lactobacilli was investigated by chair-side kits at baseline, and after 1 and 2 weeks. Data were statistically processed. A statistically significant reduction in mutans streptococci counts was observed in the test group compared with the control group. No effects on the levels of lactobacilli were noted. Daily consumption of yogurt for 2 weeks may decrease the salivary levels of mutans streptococci.