In order to measure the impact on survival of the early introduction of adequate antibiotic treatment for nosocomial bacteremia and pneumonia, a retrospective, cohort study was carried out over a period of 17 months in a 6-bed respiratory ICU. All patients presenting with a first episode of ICU-acquired nosocomial bacteremic infection (Centers for Disease Control criteria) or pneumonia [BAL culture > or = 10(4) colony-forming units (CFU)/ml or protected specimen brush culture > or = 10(3) CFU/ml] were included. The organ failure score (Fagon criteria) was recorded on the day of diagnosis. Adequate antibiotic treatment was defined by the sensitivity of each etiologic organism to at least 1 prescribed antibiotic. A total of 25 patients (Simplified Acute Physiology Score II = 44) were included in the study with pneumonia (n = 17) or bacteremia (n = 8), on average 6.5 +/- 4.6 d after admission. At the time of diagnosis, 23 patients were receiving mechanical ventilation. The overall mortality rate was 48% and was significantly associated with the length of time without adequate antibiotic treatment (p = 0.011) and the number of organ failures on the day of diagnosis (p = 0.017). Adequate antibiotic treatment only had an impact on survival if it was started within the first 24 h after sampling (p < 0.02 on Day 0 and < 0.04 on Day 1). On the day of diagnosis, a failure score > 2 was associated with increased mortality (p = 0.009). After adjusting for the number of organ failures, the length of time without adequate antibiotic treatment remained associated with mortality (< or = 2 organ failures, p < 0.02; > 2 organ failures, p = 0.05). This study suggests that, during the course of nosocomial pneumonia and bacteremia, the time at which adequate antibiotic treatment is started is a key factor influencing survival.