The purpose of the study was to assess the anti-plaque effect of chlorhexidine (CHX) in chewing gum. The 0.80 g pieces of test gum contained 5 mg chlorhexidine acetate with or without a hydrogen peroxide releasing agent. The gum base with flavouring agents but containing neither CHX nor H2O2 was used as a control. 12 dental hygiene students volunteered to participate in the 3 x crossed-over double blind clinical trial. During the 4-day test periods, no other oral hygiene measures were allowed than chewing 2 pieces of gum at the time for approximately 10 min, 5 times daily. Between test periods, meticulous mechanical oral hygiene measures were practised for 3 days. At the beginning and at the end of each test period, the quantity of plaque was assessed using the plaque index, plaque wet weight, and the area of plaque on the tooth surface as criteria. The results indicated that both CHX gums completely inhibited the increase in plaque index and plaque weight. With regard to area of plaque, the difference between the 2 test gums and the control gum was less marked but still present. The test persons subjectively assessed the gum base to have a poor cleansing effect but also the least unpleasant taste. It was concluded that use of both the chlorhexidine gum and the gum-containing chlorhexidine in addition to the hydrogen peroxide releasing agent had an excellent plaque growth inhibiting effect during the 4-day test periods.