The pressure produced by expanding aural cholesteatomas has been implicated as a causal factor in the induction of osteoclastic resorption of adjoining bone. This concept is supported by observations of osteoclastic bone resorption produced by expansive tympanic implants. We induced osteoclastic bone resorption in gerbils with tympanic implants of autologous and homologous cartilage, silicone rubber, and Teflon, which exerted pressure only by forces of gravity and surface tension. We estimated that the pressure exerted by these implants ranged from 2.1 X 10(-3) to 8.0 X 10(-3) dynes/sq cm (1.6 to 6.0 mm Hg). These pressures are within the range of pressures known to be exerted by cholesteatomas.