Amine fluoride-stannous fluoride mouthrinse was tested in a double-blind cross-over clinical trial on 16 healthy subjects. Chlorhexidine mouthrinse prepared in the same colour and taste was used as the control. After a preparatory phase of 2 weeks, during which the subjects' plaque and gingival indices were reduced to zero by professional cleaning, 1-week test periods without mechanical cleaning were started in random order. The fluoride test solution did not prevent plaque accumulation and growth of salivary S. mutans and lactobacilli as did chlorhexidine. Furthermore, the plaque wet weight was statistically highly significantly greater during test periods of fluoride rinsing than during the chlorhexidine phase. The cleansing effect, as subjectively estimated by questionnaire, was in favour of chlorhexidine, but discolorations of teeth were assessed as significantly worse during chlorhexidine periods. Neither of the test solutions showed any effect on salivary flow rate, pH, buffering capacity, or lysosomal enzyme activity.