Rational selection of antimicrobials involves working through an information overload. Spectrum, laboratory sensitivity data, clinical trial data, tissue tolerance, possibility of synergism or antagonism with another antimicrobial, route and frequency of administration, withdrawal time, cost, and label vs. extra-label use must be considered. This paper includes suggestions for evaluating some of these areas, with an emphasis on comparing and contrasting the aminoglycosides with other selected antimicrobials. Evaluation of using characteristics of antimicrobials to guide drug selection is the main focus of this paper. The evaluation of clinical trials for antimicrobial selection is not addressed, but should be included in the final selection decision.