The aim of this double-blind cross-over study was to investigate plaque accumulation after the use of the pre-brushing rinse Plax, compared to placebo. 10 volunteers underwent 2 treatment periods of 1 week, separated by a wash-out period of 1 week. At the start of each study period, professional tooth-cleaning was performed. On days 2, 4, and 7 of each treatment period, periodic identical photographs after plaque disclosure were taken for planimetric analyses of plaque extension on canines, premolars. During each treatment period, the subjects were supervised when rinsing twice daily for 30 seconds with 15 ml of placebo or Plax, followed by brushing. The subjects performed a standardized poor brushing technique without toothpaste. No significant differences were noted between placebo and Plax for plaque extension on days, 2, 4 and 7. The results show that buccal plaque growth is equal after 2x daily rinsing with Plax and placebo in subjects performing a poor oral hygiene.