The hyper-modified nucleoside Q (queuosine) is exclusively located in the wobbling position of anticodons of tRNATyr tRNAHis, tRNAAsn and tRNAAsp that recognise codons NAUC (ref. 1). Queuosine and its hexose-containing derivatives are widely distributed in microorganisms, animals and plants. We confirm here the chemical structure of queuosine as 7-(3, 4-trans-4, 5-cis-dihydroxy-1-cyclopenten-3-ylaminomethyl)-7-deazaguanosine (Fig. 1). The unique structural features of Q are the unusual cyclopentenediol side chain and the 7-deazaguanine ring. Queuosine is one of the most complicated modified nucleosides found thus far.