At public health, there is increasingly interest on evaluating the possibility of human intoxication by biotoxins from blue-green algae, mainly the hepatotoxins from the microcystin group. Microcystin, a monocyclic heptapeptide, is mainly produced by a cyanobacteria called Microcistis aeruginosa. It is characterized by a few variable amino acids, from which two of them have an unusual structure and play an important role in the hepatotoxicity of the microcystin. Although human illnesses include gastroenteritis, allergic or irritative reactions, and neurotoxicity, the main target of this toxin is the liver. Inside the hepatocytes, microcystins are carried by the transportation system of the bile acid, inhibiting the activity of the protein phosphatase in the cytoplasm. This inhibition causes a morphologic change in the plasmatic membrane because of the hyperphosphorylation of cytokeratins, and also the tumoral promotion by the hyperphosphorylated proteins. The techniques used in the detection and quantification of the microcystins in the environment include liquid chromatography, bioanalysis of mice, and immunoenzymatic tests using mono and polyclonal antibodies against those toxins. The latter has been remarked because of its practicality and its high sensibility.