Evidence is presented which confirms the structures of the five metabolites as shown in 1-5. The absolute configuration of compounds 1 and 2 was established; for compound 5 the absolute configuration was established at position 12 only. Strains of Aspergillus ustus (Bainier) Thorn and Church were isolated from stored foodstuffs in the course of a continuing search for toxigenic fungi. Maize meal cultures of A. ustus C.S.I.R. 1128 were found to cause acute toxicosis in day-old ducklings. The toxic principles were quantitatively extracted from the mouldy maize meal and systematic fractionation, guided by bioassay led to the isolation of austamide as one of the active components. The structural elucidation of austamide (4) and of prolyl-2-(1',1'dimethylallyl)tryptophyldiketopiperacine (1)* has been briefly reported. The detailed structural and stereochemical studies as well as the structures of three new metabolites, viz 12,13-dihydroaustamide (5), 12,13-dehydroprolyl-2-(1',1' dimethylallyl)-tryptophyldiketopiperazine (2) and of 10,20dehydro[l2,13-dehydroprolyl-2- l',l'-dimethylallyl)tryptophyldiketopiperazine] (3) are described herein.