['To determine if there is a statistically significant difference in the time to clinical stability (TCS) between those patients with moderate-to-severe (MTS) community-acquired pneumonia (CAP) who received their antibiotics within 4 h and those who received their antibiotics after 4 h.', 'Prospective observational study.', 'A large metropolitan teaching institution with 62,000 annual emergency department visits from May 1999 through January 2001.', 'Patients were > or = 21 year with MTS CAP as defined by the Pneumonia Patient Outcomes Research Team (PORT).', 'Triage-to-needle time (group 1, 0 to 240 min; group 2, 241 to 480 min; and group 3, > 480 min) was the independent variable, and TCS was the dependent variable. Our hypothesis was that door-to-needle time < 4 h would result in TCS reduction of 0.5 days.', 'Statistical analysis was performed using the two-tailed Student t test, analysis of variance, and multiple linear regression; p < 0.05 was considered significant.', 'Four hundred nine patients with MTS CAP achieved clinical stability during their hospital stay. Fifty-four percent of patients received antibiotics within 4 h. The mean time to receiving antibiotics was 131.46 min (2.19 h) in group 1, 335.52 min (5.59 h) in group 2, and 783.98 min (13.07 h) in group 3. Mean TCS was 3.19 days in group 1, 3.16 days in group 2, and 3.29 days in group 3. There were no statistically significant differences in TCS between the study groups.'] Does early administration of antibiotics shorten time to clinical stability in patients with moderate-to-severe community-acquired pneumonia?