OBJECTIVE: To investigate the effect of a chewing gum containing probiotic bacteria on gingival inflammation and the levels of selected inflammatory mediators in gingival crevicular fluid (GCF). MATERIAL AND METHODS: Forty-two healthy adults with moderate levels of gingival inflammation entered a double-blind placebo-controlled study design. The subjects were randomly assigned to one of three parallel arms: Group A/P was given one active and one placebo gum daily, Group A/A received two active chewing gums, and Group P/P two placebo gums. The chewing gums contained two strains of Lactobacillus reuteri: ATCC 55730 and ATCC PTA 5289 (1 x 10(8) CFU/gum, respectively). The subjects were instructed to chew the gums for 10 min over the course of 2 weeks. Bleeding on probing (BOP) and GCF sampling were conducted at baseline and after 1, 2 and 4 weeks. The levels of IL-1beta, TNF-alpha, IL-6, IL-8 and IL-10 were determined using luminex technology and multiplex immunoassay kits. RESULTS: BOP improved and GCF volume decreased in all groups during the chewing period, but the results were statistically significant (p<0.05) only in Groups A/P and A/A. The levels of TNF-alpha and IL-8 decreased significantly (p<0.05) in Group A/A compared with baseline after 1 and 2 weeks, respectively. A non-significant decreasing tendency was also observed concerning IL-1beta during the chewing period. The levels of IL-6 and IL-10 were unaffected in all groups after 1 and 2 weeks. CONCLUSIONS: The reduction of pro-inflammatory cytokines in GCF may be proof of principle for the probiotic approach combating inflammation in the oral cavity.