As thrombin is a known stimulator of retinal glial and pigment epithelial cells, we performed a pilot study to evaluate the use of thrombin as adjunctive mitogen therapy in vitreous surgery for full-thickness macular holes. Macular hole surgery was performed on 25 eyes of 24 consecutive patients with stage II, III, or IV macular holes. After removal of the posterior hyaloid, peeling of epiretinal membranes, and fluid-air exchange, 0.05 mL or 0.1 mL of thrombin (100 units/ mL) was placed over the macular hole. After infusion of a gas tamponade, the patient's head was kept in a supine position for 1 hour, and then was kept in a prone position for approximately 2 weeks. Closure of the macular hole with one procedure was achieved in 80% of the eyes. Sixty-five percent of the eyes with a closed macular hole achieved a visual acuity of 20/40 or better. Postoperative inflammation was present in all eyes, and a small hypopyon developed in 28% of the eyes. Thrombin therapy failed to markedly increase the success rate of macular hole surgery.