The aim of the present study was to determine, in vitro, the antimicrobial effect of plant extracts and propolis in saliva samples of 25 periodontally healthy subjects and 25 subjects with chronic periodontitis. One saliva sample from each subject was collected and spread on the surface of trypticase soy agar plates. Paper filter discs containing clove, sage, propolis, chlorhexidine 0.12% (positive control) and distilled water (negative control) were placed onto the plates, and incubated anaerobically for 72 hours. Significant differences in the antimicrobial effects of the different substances were tested using paired t-tests and the Spearman correlation coefficient, while differences in the effects of the extracts in periodontally healthy and diseased subjects were tested using Student's t-test. The highest means, in terms of size of microbial inhibition zones (cm) were obtained with chlorhexidine, followed by pure propolis, clove, and sage in subjects with periodontal health (1.35 +/- 0.22, 1.20 +/- 0.20, 0.94 +/- 0.14 and 0.44 +/- 0.38, respectively) or disease (1.38 +/- 0.23, 1.17 +/- 0.21, 0.94 +/- 0.07 and 0.78 +/- 0.07, respectively). There was a positive correlation between the inhibitory action of 11% propolis (w/v) and chlorhexidine (rho = 0.735, p < 0.001) in diseased subjects. The antimicrobial effects of clove and sage, particularly the latter, were less marked in comparison to propolis and chlorhexidine in both groups of subjects. In conclusion, propolis showed significant antimicrobial properties in saliva samples from periodontally healthy and diseased subjects, suggesting that this substance may be used therapeutically in the future to inhibit oral microbial growth.