Objectives: Several investigations demonstrated a difference in the formation of plaque between different individuals enabling the clinician to distinct between "slow" and "heavy" plaque formers. Our aim was to compare the percentage of vital micro-organisms in slow and heavy plaque formers, in different areas of the mouth, and at different teeth. Methods: 38 female and 12 male participants were included in the study. A professional tooth cleaning was performed and than the plaque formation rate observed after 8h, 24h, and 72h of undisturbed plaque accumulation using the plaque index (Silness and Löe 1964) and the plaque formation rate index (Axelsson 1990). Concomitantly plaque samples were taken and analyzed by vital fluorescence microscopy (Netuschil et al. 1989).The statistical analysis was performed using Wilcoxon-test and Mann-Whitney-test. Results: Generally, a statistically significant increase of plaque vitality with duration of plaque formation was observed. No differences in plaque vitality could be found between upper and lower jaw and between different quadrants of the mouth. At all investigation time points a higher amount of vital microorganisms was registered in heavy plaque formers when compared to low plaque formers (p Keywords: Plaque formation rate, heavy plaque formers, light plaque formers, bacterial vitality, vital fluorescence technique