The structures of the hepatotoxins of general name cyanoginosins-XY are proposed to be Cyclo-D-Ala-L-X-erythro-ρ-methyl-D-isoAsp-L-Y-Adda-D-isoGlu-N-methyldehydroAla (1) where X and Y represent variable amino acids and Adda is 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (2). The structural studies on four variant toxins utilised n.m.r. and mass spectral methods analogous to those recently used to determine the structure of cyanoginosin-LA. Cyanoginosin is a term we have recently suggested to describe a type of cyclic heptapeptide toxin of cyanobacterial origin. The cyanoginosins are produced by toxic strains of the freshwater cyanobacterium Microcystis aeruginosa, which is one of the species responsible for the poisoning of animals, including humans, that drink water from reservoirs on which the algae grow. We have recently described in detail the structure of a toxin from South Africa. We now report full or partial structures of four analogues of this toxin; three obtained from the same source and one from a bloom of the same alga found in the Malpas Dam in New South Wales, Australia.