The Groshong and Groshong PICC catheters are popular venous access devices because they are maintained with only weekly saline flushes. In a recent study, however, we found an apparent decrease in the rate of withdrawal occlusion in Groshong catheters flushed weekly with heparinized saline. However, a randomized trial is necessary to confirm this impression. In the current study as many as 66 patients will be randomized to each of two treatment arms. The Groshong catheters of one group will be flushed with saline only and the other group with heparinized saline. A comparison will be made between the frequency with which urokinase is used in the two groups to treat withdrawal occlusion during the first three months of catheterization. Groshong catheters using saline flushes will be compared to Groshong catheters using heparinized saline flushes and Groshong PICC catheters using saline flushes will be compared to Groshong PICC catheters using heparinized saline flushes. Data will be analyzed using Fisher's exact test.