Objective: The differential time to positivity (DTTP), defined as the difference in time necessary for the blood cultures taken by a peripheral puncture and through the catheter to become positive has been suggested to be useful in differentiating between catheter-related bloodstream infection (CR-BSI) and other sources of bacteremia. A DTTP of >120 mins was found predominantly in CR-BSI. The objective of our study was to investigate whether DTTP is useful for the diagnosis of CR-BSI in a medical-surgical intensive care unit. Design: Prospective clinical study. Setting: A 60-bed medical-surgical intensive care unit of a university hospital. Patients: One hundred consecutive adult patients from whom catheter(s) were to be removed for suspected CR-BSI were studied. Intervention: A blood culture (using aerobic and anaerobic culture bottles) was first taken from a new puncture site. Next, a blood culture was taken through every intravascular catheter in place. Measurements and Results: DTTP was calculated using the automated BacT/Alert blood culture system. Three patients had CR-BSI and nine patients had noncatheter-related bacteremia. Five patients had catheter-related sepsis without proven bacteremia. There was no significant difference in median DTTP between patients with CR-BSI and noncatheter-related bacteremia (2.1 hrs and 3.3 hrs, respectively; p = .6). Moreover, catheter-related sepsis in patients without bacteremia could not be detected using DTTP. Conclusion: DTTP seems not to be useful for the diagnosis of CR-BSI in a medical-surgical intensive care unit.