3 triclosan-containing dentifrices were compared in a 6-month, unsupervised tooth brushing study. The effects on plaque, gingival bleeding and certain salivary micro-organisms (mutans streptococci, lactobacilli, total counts of streptococci and total counts of micro-organisms) were evaluated. 123 subjects were divided into 4 groups according to severity of gingival bleeding index. 112 subjects completed the study. Following a 4-week pre-experimental period, using a sodium monofluorophosphate dentifrice (placebo), the subjects were assigned to use one of 3 triclosan-containing dentifrices, available on the Swedish market: Colgate Paradent (a triclosan/copolymer dentifrice) (n = 26); Pepsodent Gum Health (a triclosan/zinc citrate dentifrice) (n = 31); Dentosal Friskt Tandkött (a triclosan/pyrophosphate dentifrice) (n = 28); or to continue with the placebo (n = 27). The results revealed that Colgate Paradent reduced baseline plaque values by 39% (Quigley and Hein) over the 6-month experimental period. The corresponding values for the other modalities were: a reduction of 6% for Pepsodent Gum Health, an increase of 5% for Dentosal Friskt Tandkött, and an increase of 2% for placebo. A significant difference in the plaque levels (p < 0.05) was found between Colgate Paradent and Pepsodent Gum Health and between Colgate Paradent and placebo. The gingival bleeding index was improved in all 4 groups. A significant difference (p < 0.05) was found with respect to bleeding between Colgate Paradent and placebo (p < 0.05) at the 3-month registration. A statistically significant increase over time in total number of streptococci and total colony forming units were found for the Dentosal, Pepsodent and placebo groups, but not for Colgate.(ABSTRACT TRUNCATED AT 250 WORDS)