The toxicity of biomolecules obtained from sea anemones in vitro does not necessarily justify their function as toxins in the physiology of the anemone. That is why anatomical and physiological considerations must be taken into account in order to define their physiological role in the organism. In this work, antibodies generated to Sticholysin II, a cytolysin produced by the Caribbean Sea anemone Stichodactyla helianthus, are used as specific markers to explore the sites of production and storage of the cytolysin in the sea anemone. The immunoperoxidase staining developed gave specific dark-brown staining in tentacles and mesenteric filaments as well as in basitrichous nematocysts isolated from tentacles of S. helianthus. These results support the role of these proteins as toxins in the physiology of the anemone, especially in functions such as in predation, defense and digestion.