To explore possible relationships between the incidence of phlebitis in continuous intravenous (IV) infusions and the size and material of the catheter or needle, site of the infusion, type of solution, rate of flow of the infusion, and duration of the infusion, 29 adult patients were observed for symptoms of infusion phlebitis twice a day during the course of their IV therapy, from the initiation of the infusion of the onset of phiebitis or three days following the discontinuation of the infusion. A therminstor was used to measure skin temperature and aid in diagnosing phlebitis, Phlebitis was observed in nine of 26 patients who did not receive anticoagulants and in one of three patients who received drugs. Significant relationships were found between the incidence of phlebitis and eight-inch catheters as compared to shorter catheters and three-quarter-inch needles, polyethylene catheters as compared to Teflon catheters and steel needles, longer infusions, and slower infusion flow rates.