Abstract and figures N-ethylhexedrone (HEX-EN) is a synthetic cathinone, a hexedrone derivative, which is structurally close to other popular cathinones such as pentedrone and α-pyrrolidinohexiophenone (α-PHP). This substance appeared in Europe in October 2015, and it was detected in biological material for the first time at the Institute of Forensic Research in Krakow at the beginning of 2017. The article presents three cases in which the presence of N-ethylhexedrone in the blood of drivers was revealed. The use of liquid chromatography-mass spectrometry with different mass analyzers and in-depth analysis of mass spectra enabled the detection and identification of this compound, which was not covered by previously applied screening method. Liquid-liquid extraction was used for the isolation of N-ethylhexedrone from blood samples. The developed liquid chromatography-linear ion trap-mass spectrometry (LC-LIT-MS) method was successfully applied in the determination of N-ethylhexedrone. Blood concentrations of this compound ranged from 8 to 37 ng/ml. Despite the lack of clear symptoms in the reported driving cases, the N-ethylhexedrone effects reported on the Internet forums suggest that driving under the influence of this substance should be treated as a potential threat to traffic safety. Introduction n-ethylhexedrone (2-(ethylamino)-1-phenylhex- an-1-one; α-ethylaminohexanophenone) is a synthetic cathinone, a derivative of hexedrone, in which the me- thyl group attached to the nitrogen atom is substituted by an ethyl group (Fig. 1). Structurally it is similar to pentedrone, and also α-pyrrolidinohexiophenone (α-PHP), from which it differs by the substitution of a pyrrolidine group with an n-ethyl group. it is most commonly referred to as HeX-en, ethyl-Hex and neH by users (internationally), as well as Henio and Henryk by Polish users. n-ethylhexedrone was de- scribed for the first time in 1964 together with other derivatives of aminoketone in a patent by Boehringer ingelheim (Patent: GB1069797, 1964). This sub- stance appeared in europe in october 2015 and was frequently detected in the following year (eMcdda). its presence in Poland was probably a response to the amendment of the act of 29 july 2005 on counteract- ing drug addiction (journal of Laws 2005 no. 179 item 1485, with later amendments), which entered into force on 1 july 2015. on that date, another 114 new psychoactive substances (nPS) were placed on sched- ules of controlled substances, amongst them popular cathinones – α-PVP and pentedrone, as well as hexe- drone. nPS that are encompassed by legal control are immediately replaced by their new, uncontrolled.