Heparin, in concentrations of 250, 2,500 and 25,000 IU, was applied topically to the edge of tympanic membrane (TM) perforations, standardized in size, once daily until the perforation had closed. At 2 months, the animals were killed and the TMs subjected to otomicroscopic and light microscopic studies. The day that closure of the TM perforations was complete (median 8 days) was the same for the various heparin groups as for the sterile water-treated controls. However, regarding opacity of the healed TM area, heparin affected the TM in a dose-dependent manner. The TMs that had been subjected to the highest concentration of heparin were the most transparent and showed the least sclerosis. When compared for thickness, the TMs treated with the higher concentration of heparin were considerably thinner than those treated with the lower concentration. The sterile water-treated controls were all thicker than the heparin-treated TMs. It is inferred that glycosaminoglycan heparin improves the quality of the healed area of TM perforations.