In corneal organ culture, a contamination of sterile culture media with endotoxin is frequently found. Thus, we investigated if the presence of endotoxin affects the viability of cultured porcine corneal endothelial cells. Endotoxin in high concentrations caused morphological cell changes in porcine corneal endothelial monolayer cultures, delayed proliferation and decreased cellular esterase activity of porcine corneal endothelial cells in vitro. The toxic effect of endotoxin was modulated by the fetal calf serum content of the medium, the concentration of endotoxin and the incubation time.