In vitro antibiotic susceptibility tests are performed in order to assess whether a bacterial pathogen is susceptible to an antibiotic at therapeuticaly achiveable drug levels. Unfortunately, routine susceptibility testing may miss subtle mechanisms which cause lower levels of resistance In this case interpretive reading of the antibiogramme results combined with special tests is helpful in guessing other antibiotics to which the strain is resistant. Interpretive reading of the susceptibility testing results consists of the deduction of the resistance mechanism by routine suceptibility tests and some special tests and the inference from the deduced mechanism, other agents that are likely to be affected. When combined with intrinsic resistance mechanisms this approach would aid bacterial identification and serve as a complementary quality control for susceptibility tests. Although interpretation of the susceptibility testing results is done by the hospital microbiologist who changes the antibiogramme results accordingly, the clinicians who use these results and prescribe antibiotics frequently, should also have an idea about the epidemiological and therapeutic implications of a conferred reşistance mechanism and also the limitations of susceptibility testing in order to choose the best therapy for their patients.