Because many studies show that antibiotic therapy is effective for nosocomial pneumonia, it is necessary to have an approach to antibiotic selection to reduce mortality. Empiric therapy can be chosen, based on an assessment of patient risk factors for specific organisms and on an evaluation of the severity of illness present. Empiric regimens must be selected from a knowledge of antibiotic pharmacodynamics, as well as from an appreciation of the antimicrobial spectrum of the various antibacterials. When using such an approach, it is necessary to realize the limitations of effective therapy and to evaluate a number of relevant issues if the patient is not improving during treatment.