A case of polymicrobial sepsis occurred in a patient who had a permanent indwelling hyperalimentation catheter. Because it was undesirable to remove the catheter, quantitative bacteriologic techniques were used to determine whether the catheter was the source of sepsis. Blood drawn from a peripheral vein had 25 colonies per milliliter whereas blood drawn through the catheter had more than 10,000 colonies per milliliter. On the basis of these results, the catheter was removed. The catheter tip was found to be infected with the same organisms that were present in the blood. Quantitative bacteriologic techniques may prove useful in diagnosing catheter-related sepsis when it is undesirable to remove the catheter.