A compound lethal to mice (i.p.) was extracted from samples of Oscillatoria erythraea, four species of mollusc and one species of molluscivorous teleost collected from the south-east coast of Queensland, Australia, during and shortly after O. erythraea blooms. 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. erythraea is implicated as a potential elaborator of a CTX-like compound in the tropical marine biota.