Methods: 10 subjects participating in an environment replicating stone age during four weeks limited to food available to stone age man were enrolled. A thorough medical and dental examination was performed before and after the four weeks. At baseline and after four weeks, subgingival microbiological samples were collected at the mesiobuccal aspects of all teeth and from the dorsum of the tongue and processed by the checkerboard DNA-DNA hybridization methods. Results: Subjects had no evidence of periodontitis. Bleeding on probing (BOP) decreased from an average of 34.8% to 12.6% (p<0.001). Mean gingival index scores (Löe-Silness) at baseline and at week 4 were 0.38 and 0.43 respectively (N.S.) whereas mean plaque scores (Silness-Löe) were 0.43 and 1.42 respectively (p<0.001). Decreases in probing pocket depth (PPD) at sites from which bacterial samples were taken were found ( mean diff :0.2, 95%CI: 0.1-0.3, p<0.001). Total bacterial counts were higher at week 4 (p<0.001). Higher bacterial counts (p<0.001) were found for 62/73 species including Prevotella intermedia, Parvimonas micra, Porphyromonas gingivalis, and Tannerella forsythia, but not Aggregatibacter actinomycetemcomitans (Y4) nor Treponema denticola. Pseudomonas aeruginosa, Staphylococcus aureus, Echerichia coli, Haemophilus influenzae were found at higher counts at week 4 (p<0.001). At the tongue samples, lower bacterial counts were found at week 4 for i.e. Streptococcus mitis, Streptococcus, oralis, and Streptococcus sanguinis (p<0.01). Conclusions: Although plaque levels increased, decreases in BOP and PPDs were found. Diet restriction with abstinence of oral hygiene does not result in increased gingival inflammation but in increases of bacterial counts in subgingival samples but with decreases in counts in samples from the tongue. Acknowledgement: Supported by the Clinical Research Foundation, University of Berne.