In most patients tympanic membrane perforation spontaneously repairs itself. Nonetheless, in several cases the perforation persists due either to traumatic or phlogistic damage. Although the membrane perforation healing process has been under study for over a century there are still two contrasting theories. One of these theories asserts that repair takes place through the growth of granulation tissue while the other believes that epithelial migration is at the basis of healing. In the present study an experimental animal model (rat) was used in order to assess the staging of the natural evolution of post-traumatic membrane perforation and to characterize, from a morphological and sub-microscopic point of view, the cellular population and microstructural aspects of the extracellular matrix. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to evaluate the progress in tympanic membrane healing and to make a comparison with the most recent theories. Eighteen Sprague-Dawley rats weighing 230-260 gr of the same age (10 weeks) were used in the study. The animals were anesthetized by intraperitoneal injections of Na-pentobarbital (NembutalR) (45 mg/Kg) and, under operating microscope, bilateral perforation of the upper rear quadrant of the pars tensa was performed with a myringotomy lancet. The animals were subjected to periodic follow-ups over next 30 days. Three animals were sacrificed during each control and the tympanic membrane was removed for TEM and SEM study. On the basis of the present study the following conclusions can be drawn: a) primary healing of the lesion is through granulation tissue; b) the healed T.M. is composed of three normal layers as is the normal T.M.; c) the presence of fibroblasts in the intermediate neoformed fibrous layer leads one to conclude that its extracellular matrix is produced and organized "in situ"; d) the neoformed lamina propria has a disorganized, fibrous structure.