To the Editor,We read with great interest the article by Bommart et al.recently published in Cardiovascular and InterventionalRadiology, which reported the effectiveness of selectivearterial embolization using Onyx in patients with life-threateninghemoptysis [1]. We have several comments. Sinceits marketing, Onyx has been used for the endovasculartreatmentofintracranialaneurysmsandcerebralarteriovenousmalformations [2]. Until now, few studies have examined itsuse for peripheral applications. Onyx is a biocompatiblepolymer, which is an ethylene vinyl alcohol copolymer(EVOH) that is dissolved in an organic solvent—dimethyl-sulfoxide (DMSO). It becomes radiopaque by mixing withmicronizedtantalumpowder.WhenOnyx isinjectedintothevessels, the DMSO rapidly diffuses, and EVOH solidifies atthe tip of the catheter in a shape that conforms to the targetarea. The main advantageof Onyx is that, unlike other liquidembolic agents, such as cyanoacrylates, it does not adhere tothe endothelial wall and catheter tip, allowing better control ofdelivery over the embolization procedure [ 3].However, Onyx has some limitations that should beemphasized for use in interventional radiology, as previ-ously reported [4]. First, DMSO can cause severe vaso-spasm, which is most likely to occur in the early phase of theprocedure. This limitation may be avoided by using no morethan 0.2 ml of DMSO in the first minute of injection. Sec-ond, we find the duration of injection often time-consuming,depending of the amount of Onyx needed. This propensityis confirmed by the authors who used up to 3 ml of EVOHper patient and reported a total injection time of DMSO andOnyx up to45 minutesfor their procedure. Procedural timeoftenisofessencewhenusedonanemergencybasis,andtheuse of Onyx may lead to a loss of precious time comparedwith other faster embolic agents, such as glue, in such asetting. Third, DMSO is volatile and is excreted via respi-ration and sweat. This has a typical smell, which may last afew days. The patient should be warned to expect this. Last,Onyx is very expensive compared with other commonlyused embolic materials, and its cost increases with higherconcentrations of copolymer. Its high cost explains itsrestricted use in neuroradiology in most of the institutionsaroundtheworldandneedstobeborne inmindwhenusedinother organs. In conclusion, we think that Onyx is a verypromising, but too luxurious, embolic agent at this time forits use in peripheral indications.