Following in-depth analysis and examination, jellyfish toxins have been found to consist of a mixture of proteins, carbohydrates, and other non-proteinaceous components. What remains to be clarified is the specific chemical nature of jellyfish toxins due to their heat lability. This paper reviews current knowledge of the toxic properties of the most common Mediterranean scyphozoans (A. aurita, C. hysoscella, C. tuberculata, P. noctiluca, R. pulmo) and the activity of their venom.