I wish to report the failure of a Luer lock intravenous delivery system. During anaesthesia for a mastectomy, an intravenous fluid administration system was employed using, in part, an Avon wide bore extension set (Avon Medical, SIMS Portex Limited, Hythe, UK) connected via a Codan ‘R-Lock’ one way valve (Codan Ltd, Wokingham, UK) to an intravenous cannula. The Luer lock between the extension tubing and one-way valve was tightened using normal force. Upon opening the regulator, fluid was seen dripping from the junction between these components. Morphine had been administered into a 3-way tap upstream from the extension tubing and the amount of morphine delivered to the patient was therefore unclear. I recreated this system with fresh equipment of the same make and the leak was seen again. Although tightening the Luer lock using considerable excess force could contain the leak, I believe this represents a potential hazard. Comparing the Luer lock threads on the R-Lock one-way valve, a BD Connecta Plus 3 three-way tap (Becton Dickinson Infusion Therapy AB, Helsingborg, Sweden), a Universal luer lock cap (Universal Hospitals Supplies Ltd, London, UK) and the upstream end of the Avon wide bore extension set, revealed different patterns and thickness of thread (see Fig. 1). It is likely that, given this wide variation in design, incompatibility of the kind I have described will occur with other combinations of components. Differing designs of Luer lock. Clockwise from top left: Universal luer lock cap, BD Connecta Plus 3 three-way tap, Codan ‘R-Lock’ one-way valve, Avon wide bore extension set. There is already concern about the design of Luer lock systems for intravenous administration, particularly with regard to the security of the lock [1]. There is also the wider problem of the ubiquitous nature of the Luer design (for example, its use for neuraxial access systems and gas sampling devices) [2]. The fact that decades after its introduction, standardisation of the Luer lock has not been achieved does not offer hope for a solution to the wider problem. Thank you for bringing this matter to our attention and for giving us the opportunity to comment. The female Luer lock used on Avon wide bore extension sets is designed and manufactured to meet the requirements of British Standard BSEN1707 : 1997 (Conical fittings with a 6% (Luer) taper for syringes, needles and certain other medical equipment. Lock fittings). This standard specifies both the dimensions and performance requirements for Luer Lock connectors and is harmonised with International Standard ISO594. Compliance with this standard should ensure the compatibility of equipment manufactured by different companies. However, the standard does allow a degree of flexibility in design and this results in the different configurations seen in Dr Fletcher's photographs. The problems that Dr Fletcher encountered may relate to an isolated fault with either of the connecting parts. We have no adverse complaints or quality history relating to the Avon component and therefore we are unable to define the exact root cause of the reported problems. A. LingProduct Manager Smiths Medical Hythe CT21 5BN, UK E-mail: complaints@smiths-medical.com