The serum bactericidal test represents one of the few in vitro tests performed in the clinical microbiology laboratory that combines the interaction of the pathogen, the antimicrobial agent, and the patient. Although the use of such a test antedates the antimicrobial era, its performance, results, and interpretation have been subject to question and controversy. Much of the confusion concerning the serum bactericidal test can be avoided by an understanding of the various factors which influence bactericidal testing. In addition, the methodologic aspects of the serum bactericidal test have recently been addressed and should place this test on firmer ground. New information on the clinical utility of this test is becoming available; additional data are needed to establish more clearly the usefulness of the serum bactericidal test in specific infections. Such clinical trials from multiple centers will enable firmer recommendations for the future use of the serum bactericidal test.