The simultaneous occurrence of otosclerosis and otospongiosis in the same lesion is well documented. The logical sequence of events would seem to be softening and destruction of the bone by the otospongiotic lesion, which is subsequently converted to otosclerosis. Examination of 46 temporal bones has led us to further classify the lesion as: 1. an active lesion, both otospongiotic and otosclerotic, 2. an inactive lesion, also both otosclerotic and otospongiotic, or 3. a fibrous lesion. Hyalinization of the spiral ligament only occurs adjacent to active otospongiotic or very large otosclerotic lesions. If the lesion adjacent to the spiral ligament is inactive, there is no hyalinization. It seems illogical that a hyalinized spiral ligament will return to normal when the lesion changes from active otospongiosis to inactive otosclerosis. Otospongiotic and otosclerotic lesions are found side by side at the periphery of lesions, and both are adjacent to normal bone. These findings have implications concerning the mode of action of sodium fluoride and other medications that are under evaluation for the control of the sensorineural hearing loss due to otosclerosis.