Corneal ulcers and persistent epithelial defects (PEDs) are caused by a variety of different insults to the cornea, which includes limbal epithelial stem cell failure. PED may be resistant to healing with standard therapy such as frequent ointments and / or lubricants, particularly if there is coexistent ocular pathology. This study investigates the efficacy of therapeutic ocular surface medium (TOSM), a potential physiological tear replacement therapy, for persistent epithelial defects. TOSM is a manufactured serum substitute designed specifically to culture epithelial cells in the laboratory. It contains many essential tear components, such as growth factors. Eleven eyes of 10 patients with persistent epithelial defects (two weeks plus) without improvement with conventional therapy were enrolled in this prospective study of TOSM over one month. Healing of the PED occurred in three out of 11 eyes at one, two and four weeks respectively. At week four, two eyes were almost healed. In four of the remaining eyes, the PED area was reduced. One patient with end-stage ocular cicatricial pemphigoid with severe dry eye failed and one withdrew from the study due to mild allergic reaction.