Data of 3,097 blood culture sets processed with the BacT/Alert system in 1997 were compared to those of 3,158 blood culture sets processed with BACTEC 9240 in 1999. Agents responsible for bloodstream infections (BSI) were detected in 15.9% and 20.0% of blood cultures in 1997 and 1999, respectively. The incidence of BSI was 9.3 (1997) vs. 11.3 (1999) per 1,000 admissions. In both years, S. aureus was the most frequent isolate, followed by E. coli. Overall, the mean detection time (MDT) obtained with the BACTEC 9240 was significantly shorter than that of the BacT/Alert. Significant MDT differences were found for all organisms, except for Enterobacteriaceae (12.7 vs. 10.6 h). With both systems, over 95% positive samples were detected within 3 days, indicating that a 4-day incubation protocol may disclose most BSI agents. Thus, the added speed of the BACTEC 9240 allowed a particularly fast clinical management of septic patients.