A compound lethal to mice (i.p.) was extracted from samples ofOscillatoria erythraeafour species of mollusc and one species of molluscivorous teleost collected from the southeast coast of Queensland, Australia, during and shortly afterO. erythraeablooms. The compound was chemically indistinguishable from ciguatoxin (CTX) on the basis of solvent extraction and partitioning and silicic acid chromatography. Residues derived from toxic samples elicited signs of intoxication, death and histopathological changes in mice, consistent with extracts of ciguatoxic material. Stick enzyme immunoassay tests and thin layer chromatography assessment of extracts indicated the presence of ciguatoxin‐like polycyclic ether(s).O. erythraeais implicated as a potential elaborator of a CTX‐like compound in the tropical marine biota.