Incubation of cultured bovine pulmonary arterial endothelial cells (BPAEC) with MCTP results in covalent binding to DNA, cell cycle arrest and delayed but progressive cell death.  The mode of cell death in MCTP induced endothelial damage has not been addressed previously.  DNA damage is frequently associated with apoptosis. We have shown  apoptosis in adherent BPAEC treated with MCTP by nuclear morphology and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling.  MCTP induced increasing numbers of cells to undergo apoptosis over time beginning as early as 6 hours after exposure.