Current knowledge of CPE action is briefly summarized in Figure 1. After specific binding to a protein receptor(s), the entire CPE molecule rapidly inserts into membranes forming a complex of 150,000 Mr. Almost simultaneously with insertion, there is a sudden change in ion fluxes. The molecular events behind the induction of ion flux changes remain undefined, but might involve either direct formation of membrane pores by CPE or activation of pre-existing membrane pores. As intracellular ion levels change, cellular metabolism is affected and processes such as macromolecular syntheses are inhibited. One of the ion flux effects resulting from CPE treatment involves increased Ca2+ influx; as more Ca2+ enters the cell, morphologic damage and permeability alterations for larger molecules occur. It remains to be determined if both morphologic damage and larger permeability alterations are necessarily linked but, for example, it could be envisioned that CPE-induced Ca2+ influx causes a cytoskeletal collapse leading to altered membrane permeability. The cytoskeleton has been shown to be sensitive to intracellular Ca2+ levels and is important in normal membrane structure/function relationships. As the cumulative effects of CPE inhibit cellular metabolism, cell death occurs. The precise irreversible CPE lethal action still must be identified. As CPE-treated intestinal epithelial cells die in vivo, histopathologic damage appears. This damage results in loss of normal intestinal function causing secretion of fluids and electrolytes. This effect is clinically manifested as diarrhea. The strongly cytotoxic action of CPE clearly distinguished the action enterotoxin from STa or CT.(ABSTRACT TRUNCATED AT 250 WORDS)