In a retrospective study the tolerance to Teflon coated catheters in long-term intravenous medication was evaluated in 80 horses. Catheters were inserted into the jugular vein and remained there for 3 to 30 days (average 8.6 days). Catheters were flushed using an heparinized solution after each medication administration. The site of catheter placement was evaluated daily for swelling, pain and venous distensibility respectively. Swelling at the site of insertion was noted in 10 horses, a small subcutaneous abscess formation was identified in one horse. Fourteen sonographic evaluations were performed on 10 horses, demonstrating perivascular changes in four. Thrombus formation did not occur. In all horses the catheter could be identified floating freely within the vascular lumen. Catheter failure occurred in nearly a third of all cases either as a result of mechanical failure or of pull-out by the horse. After removal of the catheter no adverse side effects attributable to the mode of medication were noted in any of the horses. In conclusion, intravenous medication using Teflon-coated catheters is a suitable alternative to other modes of administration.