Micocystin (MC) exists in Microcystis cells in two different forms,free and protein-bound.We examined the dynamic change in extracellular free MCs,intracellular free MCs and protein-bound MCs in both batch cultures and semi-continuous cultures,using high performance liquid chromatography and Western blot.The results showed that the free MC per cell remained constant,while the quantity of protein-bound MCs increased with the growth of Microcystis cells in both kinds of culture.Significant changes in the dominant MC-bound proteins occurred in the late exponential growth phase of batch cultures,while the dominant MC-bound proteins in semi-continuous cultures remained the same.In field samples collected at different months in Lake Taihu,the dominant MC-bound proteins were shown to be similar,but the amount of protein-bound MC varied and correlated with the intracellular MC content.