The assignment of the structures (1)-(3) to janthitrems E-G, tremorgenic mycotoxins isolated from cultures of Penicillium janthinellum, is based on a detailed study of their highfield ¹H and ¹³C n.m.r. spectra. In the structure elucidation, extensive use was made of heteronuclear ¹³C-{¹H} selective population inversion (SPI) and homonuclear ¹H-{¹H} n.O.e. experiments. Several Penicillium species, including Penicillium janthinellum, are associated with ryegrass staggers, a neuromuscular disease in New Zealand which affects cattle and sheep grazing in pastures dominated by perennial ryegrass (Lolium perenne). Although Gallagher et al. reported the isolation of four tremorgenic mycotoxins, janthitrems A (C₃₇H₄₇NOₓ), B (C₃₇H₄₇NO₅), C (C₃₇H₄₇NO₄), and D (no formula given) from cultures of P. janthinellum, the structures of these metabolites have remained unknown so far as a result of their molecular complexity and instability. We now report the structure elucidation of janthitrems E-G (1)-(3) based on a detailed study of their highfield ¹H and ¹³C n.m.r. spectra. The close structural relationship between the janthitrems and the penitrems, e.g. penitrem D (4), is self-evident.