To test the plaque removing efficacy of three different toothbrushes in relation to duration of toothbrushing.The brushes studied were the Sonicare, the Braun Plak Remover (D7), and a modified Plak Control with increased speed (D9). Part 1 of the study was divided into four experiments which differed only in respect to the brushing time. The available times were 15, 30, 45, 60 seconds per quadrant. After 48 hours plaque accumulation, all subjects (n = 22) were brushed professionally using at random a brush in one quadrant (without toothpaste). Part 2 was a 3-way cross-over design in which the same three brushes were tested. In total 49, subjects participated. They were given a brief instruction on the use of each toothbrush and were allowed to get familiarized with each brush during a 2-week period. After 48 hours plaque accumulation, they brushed in a random order the four quadrants, each with a different brushing time (15, 30, 45, 60 seconds). The amount of dental plaque was evaluated pre- and post-brushing by means of the Silness & Löe plaque index at six sites around each tooth investigated.The results of Part 1 and 2 showed an increase in efficacy for all brushes varying from 1 minute per quadrant to 4 minutes per quadrant. In Part 1, the D7 was more effective than the Sonicare brush at 15, 20, 45 seconds whereas the D9 was more effective at all four brushing times. In Part 2, both the D7 and D9 were more effective than the Sonicare at the 2-minute brushing time. These differences were mainly caused by a greater plaque removal from the approximal areas.