Algal extracts of Anabaena planctonica from Lake Mulargia in Italy were tested for toxins by mouse bioassay, the Microtox system, and GC-MS and HPLC chromatography. Anatoxin-a was identified by GC-MS after derivatization with pentafluorobenzyl bromide. Hepatotoxins were also present and are perhaps related to the microcystins present in other species of Anabaena.