Objectives: In designing a clinical controlled trial for the assessment of the efficacy of oral antiseptics the selection of parameters and participants is a basic principle. The aim of this experimental gingivitis study was to determine whether correlations exist between different gingivitis parameters in distinctive populations. Methods: Three study populations were selected depending on the oral hygiene level of the participants (excellent vs 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 the participants rinsed with either a placebo or 0.2 % chlorhexidine (CHX). After 21 days, Gingival Index (GI, Löe et al. 1967), Modified Gingival Index (MGI, Lobene et al. 1986), Bleeding on Probing (BOP, Ainamo and Bay 1975), gingival crevicular fluid (GCF), and colony forming units (CFU) were assessed. The association between the parameters was tested using the Pearson correlation coefficients. Results: Statistically significant correlations were observed between GI and MGI in all groups and populations. GI and BOP as well as MGI and BOP correlated in group C. GI and GCF correlated only in group A after rinsing with CHX as did MGI and GCF. No correlations were found between GI and CFU. Conclusion: GI and MGI are the most reliable parameters regardless of the composition of the study population. For the use of BOP during experimental gingivitis, however, a mixed population is preferred. Supported by GABA International AG. Keywords: clinical trial, experimental gingivitis, mouthrinse, study population, gingivitis indices, discoloration index, gingival crevicular fluid, colony forming units