Bone resorption is a common finding in chronic otitis media with or without cholesteatoma. The etiology of bone resorption in chronic otitis media is still not clear. Bone-resorbing activity of prostaglandins (PGs) has been well known. PGE-like material has been detected in granulation tissue. However, there have been no reports on the comprehensive study of PGs in cholesteatomas or granulation tissue. The purpose of this study is to show that PGs are synthesized in the middle ear tissue and to report concentrations of PGs in cholesteatomas and granulation tissue. Samples of cholesteatoma and granulation tissues were obtained at the time of tympanomastoidectomies. Prostaglandin synthesizing activity was determined by incubating tissue with labeled arachidonic acid (precursor of PGs) and radiochromatography. Levels of PGs were determined by radioimmunoassay. Arachidonic acid metabolites produced in cholesteatoma and granulation tissue included PGE2; 6-keto-PGF1 alpha; PGF2 alpha; PGD2; and 5-, 12-, and 15-hydroxy-eicosatetraenoic acid (HETE). Levels of PGE2 were 2.6 times higher in cholesteatoma (106.8 +/- 46 ng/g) than in granulation tissue (41.0 +/- 14.3 ng/g). Levels of 6-keto-PGF1 alpha were two times higher in granulation tissue (89.0 +/- 27.0 ng/g) than in cholesteatoma. Levels of thromboxane B2 were two times higher in cholesteatoma than in granulation tissue. The results of this study demonstrate that cholesteatoma and granulation tissues actively synthesize PGs and contain high concentrations of them. Since PGs are locally active hormones, the presence of PGs indicates an active role for PGs in the pathogenesis of chronic otitis media with bone resorption.