Purpose: In many bacteriology laboratories, for testing susceptibility of bacteriato antibiotics is used disk diffusion method, but on the other hand, the manufacturers update the software for automated equipment at least one year after publication of the annual international norms CLSI recommendations, European or EUCAST published in 2013. Material and Methods: We compared the techniques, the types of material required and interpretation of inhibition zone diameters for strains isolated and identified routinely in laboratories. Results: The culture medium agar 5% sheep blood (CLSI) is replaced with defibrinated horse blood agar with5% addition of NAD (EUCAST). Sometimes micro-wafers are recommended for testing differentconcentrations of antibiotic; often the interpretation of susceptibility is different, even if the antibiotic concentration is the same. For some strains are excluded reports of sensitivity to certain antibiotics. Conclusions: during transition from CLSI to EUCAST should be taken into account all special requirements ofthe newer standard because it can combine elements of the two standards, knowing that there are oftencritical situations in which delaying bacteriological diagnosis or incorrect interpretationof sensitivity toantibiotics, can be followed by very serious effects.