Sea anemones are a rich source of cytotoxic proteins. Cytolysins comprise a group of more than 30 highly basic proteins with molecular masses of about 20 kDa. Cytolysins isolated from the sea anemone, Heteractis magnifica, include magnificalysin I (HMg I), magnificalysin II (HMg II) and Heteractis magnifica toxin (HMgtxn). These are highly homologous at their N-terminals. HMg I and II have molecular masses of approximately 19 kDa, and pI values of 9.4 and 10.0, respectively. Cytolysins isolated from other sea anemones Actinia tenebrosa (Tenebrosin-C, TN-C), Actinia equina (Equinatoxin, EqT) and Stichodactyla helianthus (ShC) exhibit pore-forming, haemolytic, cytotoxic, and heart stimulatory activities.