Central-venous-catheter-related infection is readily diagnosed by comparing simultaneous quantitative cultures of blood samples obtained via the catheter and a peripheral vein. The DuPont Isolator 1.5 (Du Pont Co., Wilmington, Del.) microbial culture tube was evaluated as an aid in diagnosing catheter-related bacteremia and fungemia in children and was found to be a reliable and convenient laboratory device for determining whether a long-term central venous catheter is a focus of infection.