Sixteen eyes with corneal blood staining were examined by light microscopy. Two corneal buttons were also studied by electron microscopy and immunohistochemistry. By light microscopy, most eyes disclosed hyphema, angle-closure glaucoma, and endothelial attenuation with marked corneal edema. Extra- and intracellular hemoglobin particles as well as intracellular hemosiderin were found mostly in the central cornea. Frequently we observed a gradient of hemoglobin degradation from the posterior to the anterior corneal stroma with extracellular hemoglobin particles being more concentrated posteriorly while hemosiderin-laden keratocytes predominated anteriorly. By electron microscopy, moderately electron-dense, amorphous material consistent with hemoglobin was found extracellularly as well as incorporated into stromal keratocytes, while highly electron-dense, membrane-bound granules, consistent with hemosiderin, were found intracellularly. There was marked necrosis of keratocytes, mainly those that were overloaded with hemoglobin. We conclude that hemoglobin diffuses into the corneal stroma across an intact Descemet's membrane. Continuous overload with hemoglobin leads to necrosis of keratocytes and irreversible corneal blood staining.