The nuclear magnetic resonance spectra of codeine, isocodeine, pseudocodeine, allopseudocodeine, neopine, isoneopine, and some of their derivatives have been studied and the patterns produced by the protons on dl rings except the N-heterocyclic ring have been analysed by first-order methods. Allylic, homoallylic, and other long-range couplings have been observed. Differences in chemical shift between protons in different isomers have been explained in terms of the anisotropy of the double bond or the aromatic ring.