Recent concerns about the clinical relevance of susceptibility testing echo those expressed previously by a number of authors.’-” These concerns are well founded and are perhaps even more important today because of the proliferation of new antibiotics and the changes in reimbursement philosophy.” Ultimately, the question becomes that raised by David Greenwood: “In vitro veritas?” The following discussion will review the role of susceptibility testing in clinical medicine with emphasis on myth versus reality. In addition, new directions for susceptibility testing that promise increased clinical relevance will be covered.