The high field 13C n.m.r. spectra of roquefortine derived from [1,2-13C2]acetate and [2,3-13C2]mevalonic acid lactone exhibit previously unobserved couplings, which shed light on the mode of incorporation of the isopentenyl moiety into roquefortine; satellite resonances for numerous carbon atoms in the tryptophan-derived portion of [1,2-13C2]acetate-labelled roquefortine, can be explained via the operation of the Krebs' cycle and the shikimate pathway.