To investigate the antibacterial activity of glycine, which is contained in remifentanil, when combined with propofol.Prospective study.Departments of anesthesiology and microbiology of a university hospital.Growth of the microorganisms Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans in propofol 1%; saline dilutions of remifentanil at one-, 10-, and 100-microg/mL concentrations; and 1:1 mixtures of propofol with remifentanil solutions was determined.Remifentanil inhibits bacterial growth in a concentration-dependent manner. The antibacterial effects were more pronounced with Staphylococcus aureus and Pseudomonas aeruginosa at cultures obtained at the fifth hour. The inhibition of bacterial growth was less influenced with Escherichia coli and Candida albicans.Propofol and remifentanil mixtures decreased bacterial growth, and combinations may reduce the infectious complications from accidentally contaminated propofol.