The aim of the present study was to assess the effects of three cyanobacterial metabolites anabaenopeptin-A (ANA-A), anabaenopeptin-B (ANA-B) and aeruginosin-B (AER-B) on biochemical responses: hemoglobin and total nitric oxide (NO) levels, protein tyrosine phosphatase (PTP) and heat shock protein 70 kDa (HSP70) ac- tivities of Daphnia magna. The results revealed that hemoglobin level was not altered when the crustaceans were exposed to the tested single metabolites, however binary and ternary mixtures increased this parameter with very strong synergistic interactions. NO level was not altered in the groups with single oligopeptides and decreased only by the highest concentration of binary mixture 1250 μg/L ANA-B+1250 μg/L AER-B and the ternary mixture with very strong synergistic effects. Each of the single tested oligopeptides increased PTP activity with the highest level at 1000 μg/L. It was also stimulated by binary mixture ANA-A + ANA-B and ternary mixture but decreased by binary mixtures ANA-A + AER-B, ANA-B + AER-B. We found that HSP70 activity was inhibited both in daphnids exposed to single tested oligopeptides, binary and ternary mixture with synergistic effects. The study suggest that natural exposure to cyanobacterial oligopeptides may induce various alterations of nitric oxide synthesis, tyrosine phosphatase activity and HSP70 production crustaceans that may lead to dysfunctions such as signal transmission in nervous system or downregulation of chaperone protein system.