The effect of tongue brushing on formation of dental plaque was studied in two groups of dental hygiene students. In one of the groups plaque formation during a 4-day period of no oral hygiene procedures was compared to a 4-day period of tongue brushing as the only hygiene procedure. In the other group tongue brushing as an adjunct to tooth brushing was evaluated on plaque formation during 7-day periods of partially ineffective tooth brushing. Both experiments failed to show any effect of the tongue brushing on plaque formation.