Two metabolites of P. leptostromijormis (phomopsins A and B) have been isolated as a crystalline mixture from a culture of the fungus on lupin seed. The mixture has been shown to be capable of inducing lupinosis in sheep and in young rats. Key steps in the isolation were the transfer of the phomopsins from crude aqueous solution to tetrahydrofuran and chromatography on macroreticular polystyrene resin. The bioassays used in monitoring fractions were based on inhibition of cell cultures and the mitosis-arresting effect of the metabolites on liver cells in vivo.