The haemolytic and peroxidative effects of crude extracts from Bartholomea annulata, a common Caribbean sea anemone, were investigated in erythrocytes isolated from NIH male albino mice. Significant concentration-dependent effects were found on both haemolysis (evaluated as release of haemoglobin) and lipid peroxidation (as a common index of oxidative damage to membrane lipids) in red blood cells. Moreover, the incubation of erythrocytes in the presence of either a general antioxidant, reduced glutathione (GSH, 50 microM), or an iron chelator, desferrioxamine (DFA, 10 microM), resulted in a significant attenuation of haemolysis in both cases. In light of these findings, the in vitro toxicological characterization of the venom, as well as the involvement of oxygen radical-mediated membrane damage as a potential mechanism of toxicity associated with haemolysis are discussed.