Objective: To investigate the influence of chlorhexidine in different concentrations when mixed with mineral trioxide aggregate gray (MTA-G) or white (MTA-W). The antibacterial effect on Enterococcus faecalis was used as the primary parameter. Method and Materials: Similar to the agar diffusion test, Mueller-Hinton agar plates were inoculated with E faecalis (ATCC 19433), and 14 groups (n = 21) were prepared. The specimens consisted of MTA-W and MTA-G, and these were enriched with chlorhexidine concentrations of 0.1%, 0.2%, 0.5%, 1.0%, 1.5%, and 2.0%. Pure MTA-W and MTA-G (each combined with distilled water) were used as controls. After incubation periods of 24 and 48 hours, the inhibiting areolae were measured. Results: Pure MTA-W, in contrast to pure MTA-G, had no bactericidal effects. With increasing chlorhexidine concentrations of up to 1.5%, a linear increase in bactericidal activity was observed. In contrast, MTA-G showed only a low self-bactericidal influence, and the antibacterial effects with increasing chlorhexidine concentrations were significantly lower than those of MTA-W (P .001). Conclusion: When mixed with distilled water, pure MTA-G revealed a low bactericidal effect against E faecalis. The use of chlorhexidine with MTA mixtures leads to an antibacterial effect against E faecalis, and within the first 48 hours, this effect is significantly higher in combination with MTA-W when compared with MTA-G. Schlagwörter: chlorhexidine, Enterococcus faecalis, microbiology, mineral trioxide aggregate