A novel toxin has been isolated from an aqueous extract of the coral reef crab Lophozozymus pictor by a combination of ion exchange and two-dimensional thin layer chromatography. The isolated toxin exhibited bioactivities similar to palytoxin (toxicity response of mice, cytotoxicity towards HeLa cells and release of potassium ions from rat erythrocytes). Unlike palytoxin it gave an intense blue fluorescence under ultraviolet light. A fluorescence scan showed that the toxin had a maximum excitation wavelength at 285 nm and a maximum emission wavelength at 355 nm. The toxin was distinguishable from palytoxin when analysed by high performance capillary electrophoresis and reverse phase high performance liquid chromatography.