G.ymnodinium breve, the Florida red tide organism, was cultured in enriched seawater medium; the toxin was extracted and a hemolytic fraction separated by column chromatography on Sephadex LH‐20–100. The circular dichroism spectra of isolated human erythrocyte membranes incubated with and without the hemolytic toxin were taken. No changes in the membranes due to the toxin were detected, indicating that membrane proteins were not affected. It was shown that the hemolytic toxin was removed from solution by the isolated membranes, indicating that the toxin was binding to the membranes.