To investigate the mode of action of Clostridium perfringens epsilon-toxin, MDCK cells were treated with purified toxin and incubated at 37 degrees C for up to 24h. Exposure to epsilon-toxin caused a time-dependent decrease in cell-cell and cell-substrate interactions. After 30min of treatment retraction of the cell body and the emission of filopodia were detectable in a number of cells. Longer exposure resulted in cell rounding and cell blebbing which reached a maximum after 5h of toxin treatment. A parallel modification in the cytoskeleton was also detected. Actin marginalization and the entanglement of microtubules and intermediate filaments were observed by fluorescence microscopy after 30min of toxin exposure. Functional alterations of the plasma membrane of MDCK cells were assessed by flow cytometry. After 10 or 30min of intoxication an increase in cell volume was detected, indicating an alteration in plasma membrane permeability. These findings provide evidence for cytoskeletal changes and plasma membrane functional alterations in the in vitro cell response to C. perfringens epsilon-toxin.