Recent concerns about the clinical relevance of susceptibility testing echothose expressed previously by a number of authors.’-” These concerns arewell founded and are perhaps even more important today because of theproliferation of new antibiotics and the changes in reimbursementphilosophy.” Ultimately, the question becomes that raised by DavidGreenwood: “In vitro veritas?” Thefollowing discussion will review the role of susceptibility testing inclinical medicine with emphasis on myth versus reality. In addition, newdirections for susceptibility testing that promise increased clinicalrelevance will be covered.