A double blind clinical trial was undertaken in order to compare the plaque inhibiting effect of SnF2 (0.2% and 0.3%) with chlorhexidine (0.1%) applied as mouthrinses in a test panel of 12 dental hygienist students. The experimental series were performed in periods of four days. The mean Plaque Index values were 0.35 and 0.2 when employing SnF2 and 0.1 when chlorhexidine was used, whereas distilled water resulted in a mean value close to 1.0. The long-term effect of a 0.3% SnF2 solution was tested in another group of five students for a period of three weeks. The two trials confirmed previous reports claiming that SnF2 is effective as a plaque inhibitor and, furthermore, that this effect could be maintained for a period of at least three weeks. The staining problem was less than in similar studies using chlorhexidine.