The purpose of the study was to compare the effects of four treatments on 'de novo' plaque accumulation. Treatments included tray application of 1% chlorhexidine gel (CHX-Gel), 0.12% chlorhexidine dentifrice-gel (CHX-DFG), a regular dentifrice (RDF) tray application, or 0.2% chlorhexidine mouthwash (CHX-MW) in a 3-day non-brushing model. The study was designed as a single blind, randomized parallel clinical trial. After professional prophylaxis, subjects abstained from all other forms of oral hygiene during a 3-day non-brushing period. Subjects were randomly assigned to one of the four test groups (CHX-Gel, CHX-DFG, RDF applied in a fluoride gel tray or rinsing with a CHX-MW). After 3 days, the Quigley & Hein plaque index (PI) and Bleeding on Marginal Probing (BOMP) index was assessed. Subsequently, all subjects received a questionnaire to evaluate their attitude, appreciation and perception towards the products used employing a Visual Analogue Scale. After 3 days, the full-mouth PI means were 0.88 for the CHX-gel regimen, 0.79 for CHX-MW, 1.16 for CHX-DFG and 1.31 for the RDF regimen. The two dentifrices (CHX-DFG and RDF) were significantly less effective than the CHX-Gel or the CHX-MW. Within the limitations of the present 3-day non-brushing study design, it can be concluded that the effect of a 1% CHX-Gel application tray is significantly greater than that of 0.12% CHX-DFG or RDF in inhibiting plaque accumulation. The 1% CHX-Gel applied via a tray and 0.2% CHX-MW rinse were comparably effective. © 2010 John Wiley & Sons A/S.