A randomized controlled study was done to determine whether the addition of heparin (1 U/mL) to peripheral intravenous alimentation solutions would affect the incidence of phlebitis and duration of patency of intravenous catheters in premature infants. Twenty-two-gauge Teflon catheters were uniformly used. One hundred five catheters infused with heparin were placed in 13 infants, and 122 catheters were placed in the control group of 13 infants. The time, nature, and incidence of complications were noted for each infusion site. Infusion of heparin was found to double the duration of patency of intravenous catheters and to reduce significantly the incidence of phlebitis. No complications related to the administration of heparin were noted. Heparinization of intravenous alimentation solutions should therefore be considered in premature infants as a means of reducing the work load and incidence of complications associated with peripheral lines.