Some anaesthetic agents are known to inhibit microbial growth. The aim of this in vitro study was to investigate possible antimicrobial effects of two frequently used agents in intensive care units, dexmedetomidine and midazolam. Antimicrobial effect was tested on Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa by broth microdilution method. Midazolam showed inhibitor and bactericidal effect on S. aureus at concentrations 256 mmicrog x ml(-1) and 512/microg x ml(-1) respectively and on E. faecalis at concentrations 128 microg x ml(-1) and 256 microg x ml(-1). Dexmedetomidine demonstrated inhibitor effect on S. aureus, E. coli and P aeruginosa at concentrations 32 microg x ml(-1), 16 microg x ml(-1) and 16 microg x ml(-1) respectively. Midazolam had inhibitor and bactericidal effects on S. aureus and E. faecalis. Dexmedetomidine had only inhibitor effects on S. aureus, E. coli and P aeruginosa. Further studies are needed to determine the antimicrobial mechanisms and clinical applications.