The production of secondary metabolites by cyanobacteria is extensively varied. Anabaena spp. have been shown to produce the toxins saxitoxin, anatoxin-a, anatoxin-a(s), cylindrospermopsin and microcystin. In this study we show cytotoxicity associated with Anabaena circinalis 131C that could not be attributed to its high saxitoxin content. Analytical, ELISA and enzymatic methods excluded the presence of other known cyanobacterial toxins leading to the suggestion of novel toxicity.