This article evaluates the relative effectiveness of quality improvement interventions on increasing the time to antibiotic administration after a diagnosis of pneumonia. Clinical data were abstracted from the medical records of 17,040 Medicare beneficiaries discharged from one of 215 acute-care hospitals across 15 states. Thirteen Quality Improvement Organizations collected data on hospital quality improvement interventions from each hospital in this study. Medicare discharges between January 1997 and January 2002 define the study period. Most hospitals implemented multiple interventions to improve pneumonia care. Only 3 individual interventions were found to be effective in increasing time to antibiotic administration. Data feedback and benchmarking and medical records checklists had a positive effect on time to antibiotic administration. Administrative support by itself had a negative effect on the quality indicator. Although several combinations of interventions were also found effective, generalizations about the use of multiple interventions in quality improvement are difficult to make from retrospective studies.