A randomized controlled study was done to determine whether the addition of heparin, in very low concentration (0.25 U/ml), to fluids administered through an umbilical artery catheter (UAC) would affect the duration of catheter patency. UAC occlusion occurred in 2 of 15 patients in the heparin group and in 11 of 15 patients in the control group (p = 0.001). Using life-table analysis, the functional life span of UAC was estimated. On day 8, 100% of UACs in heparin group and 9% of UACs in control group were patent (p <0.05). Coagulation profile remained unaltered after addition of heparin compared with that before the start of the therapy. There was no difference in the incidence of subependymal intraventicular hemorrhage between the two groups. It is concluded that heparin in such low concentration is effective in prolonging duration of UAC patency without causing adverse effects.