Recently, assays based on living organisms have become a frequently used tool in toxicity assessment of environmental samples containing cyanotoxins. The aim of this study was to determine the sensitivity of different organisms from commercially available toxkits to three commonly detected cyanotoxins: microcystin- LR, cylindrospermopsin, and anatoxin-a. Cyanotoxins were used in purified forms, the highest concentration tested was 4 μg/ml. The most pronounced toxic effects were observed in the presence of cylindrospermopsin, with the lowest LC₅₀ (24h LC₅₀ = 0.27 μg/ml) estimated for the crustacean Thamnocephalus platyurus. On the contrary, anatoxin-a was found to be toxic only to a small degree, with the EC₅₀ only calculated for Daphnia magna (24h EC₅₀ = 2.09 μg/ml; 48h EC₅₀ = 1.70 μg/ml). In that case the test endpoint was manifested as an inability to swim freely rather than lethality, so it was impossible to estimate LC₅₀ values. In turn, the most pronounced toxic effects of microcystin-LR were observed in D. magna after 48-h exposure with EC₅₀ estimated at 0.97 μg/ml. The lowest sensitivity to the cyanotoxins at studied concentrations was demonstrated in acute tests for the rotifer Brachionus calyciflorus, and to some extent the algae Selenastrum capricornutum. It can be concluded, therefore, that organisms used as bioindicators vary considerably in their sensitivity to cyanotoxins and the obtained EC₅₀/LC₅₀ values are much higher than typical toxin concentrations in the environment.