The aim of this study was to test the hypothesis that xylitol, alone and in combination with fluoride, affects the salivary flow rate and micro-biota, dental plaque accumulation, gingivitis development, and the acidogenic potential of plaque. Three groups, each of 10 subjects, rinsed for 1 min 3 times daily over two 4-week periods, first with 10 ml water (control), and thereafter with either 0.05% NaF, 40% xylitol, or with 0.025% NaF plus 20% xylitol according to a double-blind controlled design. They performed habitual mechanical tooth cleaning during the first 2 weeks of each period but abstained from interdental cleaning during the final 2 weeks. While mouth rinsing was continued, all mechanical oral hygiene was discontinued the last 2 days of each period to permit plaque accumulation. The last mouth rinse was administered in the clinic before the final examination. The following parameters were assessed: (1) unstimulated and paraffin-stimulated salivary secretion rates; (2) salivary micro-biota; (3) plaque index; (4) papillar bleeding; (5) plaque pH response to sucrose, and (6) lactate formation by dental plaque. No statistically significant differences in any of the parameters were found. In conclusion, three daily mouth rinses with fluoride and xylitol, separately or in combination, did not affect the salivary flow rate or micro-biota, dental plaque accumulation, gingivitis development, or the acidogenic potential of plaque.