This paper reports measurements of oral retention and intra-oral distribution of triclosan in man after use of an antiplaque toothpaste slurry containing this antibacterial. Determinations of triclosan were made by high-performance liquid chromatography. It was shown that 38% of the triclosan in a 1-gramme dose of toothpaste (0.50%, w/w triclosan) and 62% of a 3-gramme dose was retained. Triclosan was detected and measured in plaque and this antibacterial was also present in saliva. Levels of approximately 20–30 μg triclosan/ml of saliva were measured 5 min after toothpaste use and these had fallen to approximately 3–4 μg/ml 2 h later. A significant inhibition of plaque acid production is shown to follow use of the antiplaque dentifrice.