To maintain the patency of a peripherally inserted central catheter (PICC) line, it has been common practice to use 100 units of heparin as a flush. In this study, it was hypothesized that 10 units of heparin would maintain the patency of the PICC line as effectively as 100 units. To test this hypothesis, 46 patients who had PICC lines placed were retrospectively identified. Twenty patients received 100 units of heparin and had a PICC indwelling time ranging from 4 to 52 days (mean = 12 days) for a total of 314 indwelling days. Twenty-six patients received 10 units of heparin and had PICC indwelling time ranging from 2 to 54 days (mean = 11 days) for a total of 440 indwelling days. In two patients who received 100 units of heparin, PICC lines clotted after 2 days and 16 days, respectively. In four patients who received 10 units of heparin, PICC lines clotted after 5, 9, 29, and 36 days, respectively. Given the fact that this study was retrospective and uncontrolled, a statistical analysis was inappropriate; however, as a descriptive study, there appears to be evidence to support the original hypothesis. A controlled, blinded study must be performed to test the hypothesis statistically.