The effectiveness of amine fluoride and stannous fluoride in the prophylaxis of caries and gingivitis is well-known from the literature. The aim of this study was to assess whether these agents could be recommended for long-term use. Under conditions of a clinical double-blind study, the influence of an amine/stannous fluoride rinse on gingivitis, plaque accumulation and the composition of the supragingival plaque was tested over a period of 7 months. 102 persons with signs of chronic gingivitis participated in the study. Gingival indices (GI, SBI) and plaque indices (PlI, API) were recorded at baseline, after 3.5 and 7 months. The composition of the supragingival plaque was evaluated by dark-field microscopy. During the 7 months, the GI decreased in the test group from 1.36 to 0.95, and the SBI from 52.0% to 29.3%. The PlI fell from 1.17 to 0.68, and the API from 61.3% to 50.6% (p < 0.001). No significant changes were recorded in the control group. In the test group, the proportion of cocci in the plaque increased from 58.4% to 68.9% (p < 0.001) while the proportion of rods and other plaque bacteria underwent a significant decrease (p < 0.001). The microflora was stable in the control group throughout the study period. No side-effects of the drug were reported by the probands. The results suggest that long-term use of the amine/stannous fluoride rinse is of benefit to gingival health.