We studied the healing of trabeculectomies in rabbits with photographs, fluorescein filtration and histological sections. Initially all except 1 developed proven filtration. However, vigorous fibroblastic proliferation (and collagen production) from the subconjunctiva, uvea and sclera combined to close off the fistula by day 14. Groups of eyes treated with 8 mg of prednisolone injected subconjunctivally at operation showed slightly delayed wound healing but by day 30 there was little difference between treated and untreated groups. The steroid treated eyes had complications ranging from endophthalmitis in 1 eye to tissue necrosis in 3 eyes.