Mouthwashes containing 0.3% or 0.15% triclosan in combination with 1.5% sodium lauryl sulfate (SLS) produced a significant reduction in plaque formation in a test panel of 11 students who refrained from oral hygiene during the test periods, during which they rinsed twice daily with different mouthwashes. Pl.I. was evaluated after each test period. A mouthwash containing only 1.5% SLS inhibited plaque to almost the same degree. In both cases, the major effect was on the buccal/lingual surfaces, where score 2 was changed to score 0. Addition of triclosan appeared to reduce the untoward side-effects of mouth-washes containing SLS alone (i.e. desquamation and a burning sensation in the mouth).