Red Tide is a world-wide phenomenon and refers to the sudden appearance of marine organisms that produce discolored water and various problems. In Florida, the red tide organism Gymnodinium breve is associated with mass marine mortalities, with economic costs estimated at $20 million and $17 million for the 1971 and 1973-74 outbreaks, and with environmental health hazards. These include respiratory problems and skin irritations that may affect thousands near beaches that have been littered with millions of dead fish. A material (provisionally called "aponin"), isolated from red tide water, is cytolytic toward G. breve in the laboratory, and is elaborated by the responsible organism, Gomphosphaeria aponina. It is proposed to extend the knowledge about aponin properties to the potential management of red tide outbreaks under selected conditions. It is necessary to be able to predict the effect of salinity, pH, and nutrients on the growth of G. aponin production, and the effect the material would have on ecologically significant organisms other than G. breve. A few organisms have been investigated, and it is proposed to extend the investigation to other organisms. In addition, it is proposed to pursue the characterization of the material and to synthesize aponin-like materials.