In 1997 and 1998, ciguatera cases were reported in Sibuyan Island Philippines and confirmed by the Philippine Department of Health. In response to this, sampling sites for Gambierdiscus toxicus were established in three areas with varying dominant macroalgal species last August - October 1999. The sampling sites were located in Cajidiocan- San Fernando, Sibuyan Island with the following dominant algal species : a) nearshore intertidal zone - Sargassum polycystum b) offshore coral reef - Actinotrichia spp. c) offshore reef area - Gelidiella spp. The G. toxicus cells were observed from algal samples taken from offshore coral reefs while G. toxicus were absent from algal thalli from nearshore area. The cell densities in Actniotrichia and Gellidiela thalli varied from nil to 7.0 cell/sq cm. The suspension of silt from the main Sibuyan Island during heavy and frequent rainfall in southwest monsoon months most likely influenced the marked distribution of G. toxicus in the surrounding coastal waters.