A stomach content analysis was undertaken to determine the changes in the natural diet of the green abalone Haliotis fulgens as they relate to the 1997 to 1998 El Niño event at 2 sites along the central coast of the Baja California Peninsula. The index of relative importance of each identified food item was calculated, and Levin's index was used to determine the breadth of the diet. A total of 20 macroalgal species, 1 seagrass species, and 4 invertebrate species were observed from March 1997 to July 1998. The main constituents of the diet of H. fulgens before the 1997 to 1998 El Niño were Macrocystis pyrifera, Phyllospadix torreyi, and Cystoseira osmundacea. During and after, the principal items were Sargassum sp., Spatoglossum howelli, Cystoseira osmundacea, Dictyota sp., Gelidium sp., and Phyllospadix torreyi. Diet breadth of abalone diet was greater during and after El Niño 1997 to 1998 than before. Our results show that green abalone diet varies with the availability of the food source; therefore, El Niño events caused a major shift in diet related to changes in the local algal flora.