Prolonged postoperative hypotony is a severe complication frequently associated with trabeculectomies performed with a single perioperative application of Mitomycin C. We performed an animal experiment using 8 pigmented rabbits applying different concentrations of Mitomycin C, ranging from 0.05 to 1.0 mg/ml, under the conjunctiva on the intact sclera for 5 minutes. The eyes were examined by light and electron microscopy after 4 weeks. The nerves within the ciliary body in areas adjacent to the region of treatment showed toxic effects related to the concentrations of Mitomycin C applied. In cases where small concentrations were used, only the unmyelinated nerves were damaged with the myelinated remaining intact. In eyes treated with high concentrations, both groups of nerves exhibited severe signs of destruction. This effect is likely to compromise the production of aqueous humor in rabbits, and possibly also in humans.