This paper reviews the toxicity and tumor-promoting properties of microcystins. Methods for screening and/or identification of microcystins in environmental samples are discussed and compared. Specific emphasis is placed on newly developed extraction/detection methods, e.g., solid phase microextraction (SPME) technique, and capillary electrophoresis coupled with laser-induced fluorescence detection. The results of a kinetic analysis of the effects of microcystins on phosphorylase-a binding to phosphatase-2A using a surface plasmon resonance biosensor are also presented.