cyanobacteria contamination of water has become a growing public health problem worldwide . 
 microcystis aeruginosa is one of the most common toxic cyanobacteria . 
 it is capable of producing microcystins , a group of cyclic heptapeptide compounds with potent hepatotoxicity and tumor promotion activity . 
 the present study investigated the effect of microcystic cyanobacteria on primary cultured rat hepatocytes by examining mitochondrial membrane potential ( mmp ) changes and intracellular reactive oxygen species ( ros ) formation in cells treated with lyophilized freshwater microcystic cyanobacteria extract ( mce ) . 
 rhodamine 123 ( rh-123 ) was used as a fluorescent probe for changes in mitochondrial fluorescence intensity . the mitochondrial rh-123 fluorescence intensity in mce - treated hepatocytes , examined using a laser confocal microscope , responded in a dose- and time - dependent manner . 
 the results thus indicate that the alteration of mmp might be an important event in the hepatotoxicity caused by cyanobacteria . 
 moreover , the parallel increase of ros formation detected using another fluorescent probe , 2',7'-dichlorofluorescin diacetate also suggests the involvement of oxidative stress in the hepatotoxicity caused by cyanobacteria . the fact that mmp changes precede other cytotoxic parameters such as nuclear staining by propidium iodide and cell morphological changes suggests that mitochondrial damage is closely associated with mce - induced cell injury in cultured rat hepatocytes.imagesfigure 1figure 2figure 3figure 4figure 5figure 6