Objectives: Several indices are recognized as reliable for scoring plaque and gingivitis during evaluation of mechanical and chemotherapeutic antiplaque procedures. The aim of this investigation was to determine whether correlations exist between different plaque parameters as well as between plaque- and gingivitis parameters in distinctive populations. Methods: Three study populations were selected depending on the oral hygiene level of the participants (excellent / modest). Population A (excellent) consisted of 39 dental students, B (modest) of 38 participants from a local population, and C was a mixed population (A+B, n=77). During a 21 day experimental gingivitis study using parallel group design the participants rinsed with either a placebo or 0.2 % chlorhexidine (CHX). After 21 days, plaque indices according to Silness & Löe (1964, PlI) as well as to Quigley & Hein modified by Turesky (1970, QHI) were evaluated. Furthermore the Gingival Index by Löe (1967, GI), and the Modified Gingival Index by Lobene et al. (1986) (MGI) were assessed. For statistical analysis the Pearson correlation coefficient was used. Results: Statistically significant correlations were observed between PlI and QHI in all groups and populations. A correlation between plaque recording systems and gingivitis parameters (GI, MGI) was only shown for population A, and for the CHX-groups in population B and C. Conclusions: For assessment of plaque accumulation PlI and QHI are the most reliable parameters regardless of the composition of the study population. In determining associations between plaque accumulation and inflammation, populations with excellent oral hygiene are advisable. Supported by GABA International AG Keywords: clinical trial, experimental gingivitis, mouthrinse, plaque index, gingivitis index