Summary. A group of highly toxic compounds was isolated from galled seedbeads of annual ryegrass (LoHiim rigidum Gaud.) containing Coryncbactcrium rathayi. Purified extracts were resolved by reverse-phase high-performance liquid chromatography into eight main fractions which have been parLially characterised and shown to be toxic to nursling rats. A mixture of Ihe toxins also produced clinical signs and brain lesions in Iambs consistent with annual ryegrass toxicity. The name 'corynetoxin' is tentatively proposed for the series, individual members being designated according to their order of elution from the high performance liquid chromalography column as corynetoxins 1 to 8. The two main fractions are corynetoxins 3 and 4 of which the former has been crystallised. They appear to be of glycolipid character, 3-hydroxyheptadecanoic acid and a C,i amino sugar being identified among the hydrolysis products of corynetoxin 3. and heptadec-2-enoic acid and a Cu amino sugar from corynetoxin 4.