From the viscera of a green turban shell Turbo marmorata collected at an Okinawan coral reef, a water soluble toxin resembling saxitoxin was obtained. The chromatographic behavior of the toxin on columns of ion exchange resin, silicic acid, and Sephadex LH-20 coincided well with that of saxitoxin. Thin-layer chromatography with two solvents also could not differentiate between the two toxins. In qualitative chemical tests, the green turban toxin was positive to Jaffe and Weber reagents, as was saxitoxin. As regards the biological activity, the two toxins gave practically the same dose-death time curves when tested on mice. From all these results it was concluded that the green turban toxin is identical with saxitoxin. This may be the first report of the occurrence of saxitoxin in a mollusk associated with coral reefs.