An antiplaque toothpaste containing 0.2% (w/w) triclosan significantly inhibited overnight plaque growth in 12 human volunteers. After use of a 1 g quantity of the toothpaste containing 0.2% (w/w) [3H]-triclosan, 36.3 +/- 1.4% of the triclosan was retained. The mean concentration (+/- s.d.) achieved in saliva 5 min after toothpaste use was 8.16 +/- 2.50 micrograms g-1. The saliva decay curve for triclosan was consistent with a two phase model with t1/2 values of 0.45 h and 2.42 h, respectively. Triclosan was present in bacterial plaque for at least 8 h after dosage and in the oral mucosa for at least 3 h.