We have identified a new compound in capsules marketed as plant feeders available from internet suppliers. It is apparent from internet forums that these so-called plant feeders are being used as recreational drugs. The material is identified as being 3'-fluoromethcathinone. The compound in the capsule was identified by GC-MS, 1H, (13)C and (19)F NMR as well as FTIR. Other materials identified in the tablet were caffeine and a methylamine salt. The exact position of the fluorine in the fluoromethcathinone was determined by comparison with materials synthesised in our laboratory. Internet-based companies are known to sell 4'-fluoromethcathinone (flephedrone). We present GC-MS data for the three isomers of fluoromethcathinone and their N-acetyl derivatives and provide a rapid method for determining the positional isomers of fluoromethcathinone using FTIR or (19)F NMR.