Additive, synergistic or antagonistic effects of various types of cyanotoxins have so far not been investigated. The aim of this study was to assess the potential synergistic effects of microcystin-LR and anatoxin-a on immune cells isolated from the common carp (Cyprinus carpio L.). Cytotoxicity of the toxin mixture to leukocytes, its influence on lymphocyte proliferation, as well as phagocytosis and intracellular production of reactive oxygen species by phagocytes were assessed. The membrane integrity in leukocytes decreased significantly only at the highest concentration used of the toxins in the mixture. The toxins caused oxidative stress in fish leukocytes by increasing the generation of reactive oxygen species. Moreover, the suppressive effects of toxins on the essential immune cell functions: lymphocyte proliferation and phagocytosis were observed. These results clearly demonstrate that the toxins have an immunotoxic influence on the different parameters of carp immune cells.