Application of autocorrelated homonuclear (COSY) and proton-carbon chemical shift correlation two-di­mensional nmr experiments to the problem of assigning the 'H- and "C-nmr spectra of phenanthro[4,3-aldi­benzothiophene fails despite their considerable utility in the assignment of the spectra of the smaller phen­anthro[b]thiophenes. The failure of these techniques in the case of phenanthro[4,3-aldibenzothiophene is pre­dominantly due to the inability of the COSY spectrum to provide the means of subgrouping the proton reso­nances into their component spin subsystems. Two-dimensional relayed coherence transfer nmr experiments which first established coherence between vicinally coupled protons which is then transferred to the carbon spins which are ultimately observed circumvent these problems. The application of two-dimensional relayed coherence transfer to phenanthro[4,3-a]dibenzothiophene is described, the technique leading to the sub­grouping of all five of the proton spin subsystems and thus providing a means of beginning the total assign­ment.