In our continuing search for bioactive substances from marine organisms, four novel alkaloids, pinnatoxins, halichlorine, pinnaic acids and norzoanthamine were isolated. The structures and functions of these marine alkaloids are described here.Pinnatoxins, potent shellfish poison, were purified form the Okinawan bivalve Pinna muricata. Pinnatoxins activate Ca2+ channel. Especially, toxicity of pinnatoxins B, C is as significant as that of tetrodotoxin. Halichlorine was isolated from the marine sponge Halichondria okadai. This compound inhibits the induction of VCAM-1 at IC50 7 mu g/ml. Drugs that block VCAM-1 may be useful for treating coronary artery diseases, angina and noncardiovascular inflammatory diseases. Pinnaic acids, cPLA(2) inhibitor, were also obtained from the Pinna muricata. Interestingly, the structures of pinnaic acids are closely related to that of halichlorine. Norzoanthamine hydrochloride, isolated from the colonial zoanthid Zoanthus sp. which suppresses the decrease in bone weight and strength in ovariectomized mice, could be a good candidate for an osteoporotic drug.