Purpose: The aims were to evaluate a simple method to disclose a microbial shift in saliva and to investigate the short- and long-term effects of daily use of xylitol-containing chewing gums on mutans streptococci (MS) and [14C]-xylitol uptake in saliva. Materials and Methods: In a pilot set-up, saliva samples were collected from 15 healthy adults and the uptake of xylitol was compared with a specific assay determining xylitol-sensitive MS. The main study consisted of 109 schoolchildren (mean age 9.9 years) who volunteered after informed consent. The children were randomly allocated to a test or control group. The control group was given two pellets containing sorbitol and maltitol 3 times daily for 4 weeks and the test group received identical pellets with xylitol as single sweetener (total dose 6.2 g/day). Saliva samples were collected at baseline, after 4 weeks and 6 months after the intervention. The outcome measures were MS and total viable counts, proportion of MS and salivary uptake of [14C]-xylitol. Results: The pilot study disclosed a fair positive correlation (p 0.05) between the assays. The proportions of MS and salivary xylitol uptake decreased significantly in the xylitol group by 60% and 30% respectively after 4 weeks compared to baseline which was in contrast to the sorbitol/maltitol group (p 0.05). Six months after the intervention, the outcome measures did not differ significantly from baseline in any of the groups. Conclusion: A relatively high daily dose of xylitol could alter salivary microbial composition during the intervention period but no long-term impact was observed. Keywords: chewing gum, mutans streptococci, oral microflora, saliva, xylitol