Contamination of drugs is an important issue and may occur during the production, preparation and treatment process. Esmolol is a specific cardioselective beta-1-blocker without preservative used in clinical practice. In this study, it was decided to evaluate whether esmolol itself has antimicrobial activity in vitro. Antimicrobial activity of esmolol was determined by using the broth macrodilution method against bacterial strains Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Staphylococcus epidermidis (ATCC 1490) and Pseudomonas aeruginosa (ATCC 27853) in both 25 degrees C and 37 degrees C. Esmolol had no antimicrobial effect on S. aureus, S. epidermidis, E. coli and P. aeruginosa at any concentration and temperature. The lack of antimicrobial activity of esmolol is a risk for microbial growth. Therefore, infusion bags of esmolol should not be allowed to stand at room temperature for a long time and storage conditions should be monitored rigorously. It will be protective to administer drugs to patients preferably by infusion pumps instead of syringe pumps against possible contamination.