In a prospective study of 108 intravenous infusions a significant decrease was noted in the incidence of both cannula-related sepsis and cannula-related phlebitis in those patients on low dose (1000 units/1000 ml infusate) heparin given intravenously. A significant decrease in the incidence of cannula-related phlebitis was also noted in patients receiving subcutaneous low dose heparin (5000 units 8-hourly). This significant decrease may be due to inhibition of fibrin clot formation around the tip of the indwelling intravenous cannula.