The results of in vitro antibiotic susceptibility testing guide clinicians in the appropriate selection of antimicrobial drugs. It became necessary to perform the antimicrobial susceptibility testing using standardised methods. In this paper the most important steps of antimicrobial susceptibility testing, and recommendations for quality control are presented. We described the standard methods used to detect the resistance to antibiotics. In two tables we presented the factors influencing the diameters of the inhibition zones and errors wich may appear using the disk diffusion method.