A six-month, double-blind clinical study was entered into by three hundred twenty-five (325) male and female adult subjects to assess the efficacy of a dentifrice containing 0.3% triclosan (Irgacare MP, Ciba-Geigy Corp.) and 2.0% of a copolymer of methoxyethylene and maleic acid (Gantrez, ISP Corp.) on supragingival plaque formation and gingivitis, compared to a placebo dentifrice over a six-month period. Each dentifrice, the triclosan and the placebo, contained 0.243% sodium fluoride in a silica base. Only those subjects who were free of periodontal disease (no pockets > 4 mm), demonstrated a level of at least mild gingivitis (modified Loe-Silness score > or = 1.0) and had a modified Quigley-Hein Plaque Index score of > or = 1.5 were admitted into the study. Baseline plaque and gingivitis scores were used to stratify the subjects into two balanced groups. A thorough oral prophylaxis was administered to all subjects. They were then assigned either the triclosan/copolymer dentifrice or the placebo dentifrice to use for the next six months. Evaluation for gingivitis and supragingival plaque formation was made after three and six months. Evaluations made after six (6) months demonstrated a 17.0% statistically significant (at the 99% level of confidence) reduction in supragingival plaque formation was provided by the triclosan/copolymer dentifrice, compared to the placebo dentifrice. An 18.6% statistically significant (at the 99% level of confidence) reduction in plaque formation on the tooth surfaces with the highest plaque formation was provided by the triclosan/copolymer dentifrice, compared to the placebo dentifrice.(ABSTRACT TRUNCATED AT 250 WORDS)