The aim of this study was to evaluate changes in the subcellular organelles of cultured hepatocytes by laser scanning confocal microscopy during chemical hypoxia with cyanide and iodoacetate, inhibitors of mitochon-drial respiration and glycolysis, respectively. Parameter-specific fluorophores used were calcein for cell topography and membrane permeability, rhodamine-dextran for lysosomes, rhodamine 123 and tetramethylrhodamine methylester (TMRM) for mitochondrial membrane potential (Δ Ψ) and propidium iodide for loss of cell viability. During the first 30 to 40 minutes of chemical hypoxia to cultured hepatocytes, numerous surface blebs formed and cell volume increased, but Δ Ψ decreased relatively little. Subsequently, the nonspecific permeability of mitochondrial membranes increased, and mitochondria depolarized. These events were followed a few minutes later by disintegration of individual lysosomes. After a few more minutes, viability was lost as indicated by bleb rupture, gross plasma membrane permeability to calcein, and nuclear labeling with propidium iodide. Thus, the following sequence of intracellular events occurred during chemical hypoxia: adenosine triphosphate (ATP) depletion, bleb formation with cellular swelling, onset of a mitochondrial permeability transition, disintegration of lysosomes, plasma membrane failure from bleb rupture, and cell death. Any explanation of the pathophysiology of hypoxic injury must take into account this unique sequence of events.