The accuracy of differential quantitative blood culture in the diagnosis of central venous catheter sepsis was evaluated in 24 parenterally-fed patients in whom catheter sepsis was suspected. The pour-plate quantitative culture technique was performed immediately before removal of the catheter on blood drawn through the central venous catheter and a peripheral vein. If bacterial colonies in the catheter blood specimen were sevenfold more frequent than identical bacterial colonies in the peripheral blood specimen, the test was considered positive and indicative of catheter sepsis. Catheter-tip culture identified 9 of the 24 patients as positive for catheter sepsis. A positive differential quantitative blood culture result was found for seven of the nine infected catheters. Sensitivity of this test was 77.8%, specificity was 100%, and overall accuracy was 91.7%. It is concluded that differential quantitative blood culture is a reliable method for the exclusion of catheter sepsis.