This comparative clinical 9-month study was designed to examine the efficacy of amine/stannous fluoride (AmF/SnF2) (Meridol) and sodium fluoride (NaF). 150 probands with chronic gingivitis or early signs of periodontitis were divided into 3 randomised groups. Group 1 was given a NaF toothpaste and an NaF mouthrinse, group 2 AmF/SnF2 toothpaste and mouthrinse, and group 3 AmF/SnF2 toothpaste and NaF mouthrinse. The probands were examined at intervals (0, 1, 3 and 9 months) under conditions of a clinical double-blind study. The parameters recorded were the plaque index (PlI), the approximal plaque index (API), the gingival index (GI) and the mod. sulcus bleeding index (SBI). The probing depths (PD) were also measured. The composition of the supragingival plaque was evaluated by dark-field microscopy. A highly significant reduction in all clinical parameters was recorded in all 3 groups in the course of the study. The most pronounced reduction in PlI, API, SBI and PD was recorded in group 2. In the group comparison, however, no significant differences were recorded. Microbiological examination revealed a highly significant increase in cocci and a decrease in rods in all 3 groups. There was also a significant reduction in spirochetes, filaments and fusiforms in groups 2 and 3. In group 1, there was a significant fall only in fusiforms and small spirochetes. Overall, no significant difference in clinical parameters was recorded in the group comparison. However, the use of AmF/SnF2 toothpaste and mouthrinse (group 2) and, to a lesser degree, the combined use of AmF/SnF2 toothpaste and NaF mouthrinse display a favorable microbiological effect. The results from the present double-blind study reveal a reduction in gingival inflammation and supragingival plaque accumulation with a positive change in plaque flora in all groups. The reduction in potentially gingivopathogenic bacteria was slightly higher in the amine/stannous fluoride group.