The purpose of the present investigation was to study the topographical distribution of plaque formation using chlorhexidine digluconate (CH) as a mouthrinse and in oral irrigators during experimental gingivitis. Forty dental students (aged 22--26) with clean teeth and healthy gingivae abolished oral hygiene for a period of 3 weeks (Löe et al. 1965). During this period the participants were randomly assigned to one of five groups. Group A rinsed daily with 30 ml of a placebo and Group B with 30 ml 0.1% chlorhexidine digluconate. In Groups C and E a fractionated jet irrigator was used for the daily application of 600 ml placebo (C) or 0.05% CH (E); 600 ml of 0.05% CH was also used in a monojet irrigator (Group D). At the start, after 1, 2 and 3 weeks of no oral hygiene and 1 week following reinstituted oral hygiene, plaque was assessed using the Plaque Index (Silness & Löe 1964) and gingival health was scored according to the criteria of the Gingival Index (Löe & Silness 1963). The discoloration of the teeth was determined using a set of color photos. During the experiment all groups reached plaque levels that were significantly different from each other. The highest PlI were seen in the placebo rinsing group (A) following by placebo irrigation (C). Plaque was significantly reduced in the CH groups. However, rinsing group (A) followed by placebo irrigation (C). Plaque was significantly reduced in the CH groups. However, rinsing (B) formed significantly more plaque than using the oral irrigator (D, E). Group E showed the least amount of plaque. In addition, the interproximal PlI were equally low as the buccal and lingual. With CH (B, D, E), gingivitis did not develop except for some interproximals in Group B. A fractionated jet irrigator was more effective for the application of CH than rinsing.