Palytoxin is one of the most potent non-proteinaceous toxins found in nature. It was named after the original source it was isolated from, a marine invertebrate belonging to the zoantharian genus Palythoa. Since its discovery scientists have speculated on what organism produces palytoxin, and also on its biological role. We studied the palytoxin content in Palythoa colonies and its relation to the composition of the bacterial communities associated with their gastric cavities.