The assignment of structures (2)-(6) to penitrems B-F, tremorgenic mycotoxins isolated from cultures of Penicillium crustosum, is based on a detailed study of their high field 'H and l3C n.m.r, spectra. The relative configuration of penitrems B-F was deduced from the magnitude of the proton-proton coupling constants. The absolute configuration of these metabolites is based on comparisons with that of penitrem A and on the absolute configuration of penitrem D determined by the ' partial resolution ' method of Horeau.