Intravenous therapy complications with steel needles, Teflon® catheters, and silicone elastomer catheters were compared in a randomized study of 558 cannulae in 325 patients. Cannulae were inserted, cared for, and removed at 72 hours by an intravenous nurse team. The risk of phlebitis was significantly greatr with the Teflon and silicone elastomer catheters. Steel needles carried a significantly greater risk of infiltration. It was concluded that 1) steel needles are easiest to insert; their low rate ofphlebitis makes them suitable for short-term therapy; they should not be used for I.V. administration of drugs that produce tissue necrosis with extravasation; 2) silicone elastomer catheters cannot be routinely recommended because of insertion difficulty, increased phlebitis, and cost; 3) Teflon catheters are recommended for longer courses of I.V. therapy because of ease of insertion, low cost, and low infiltration rates.