Actinoporins are potent pore-forming toxins produced by sea anemones. They readily form pores in membranes that contain sphingomyelin. Molecular mechanism of pore formation involves recognition of membrane sphingomyelin, firm binding to the membrane accompanied by the transfer of the N-terminal region to the lipid-water interface and oligomerization of three to four monomers with accompanying pore formation. Actinoporins are an important example of alpha-helical pore forming toxins, since the final conductive pathway is formed by amphipathic alpha-helices. Recent structural data indicates that actinoporins are not restricted to sea anemones, but are present also in other organisms. They are becoming an important tool and model system, due to their potency, specificity and similarity to other proteins.