The serum and middle ear tissue concentration of enoxacin, a pyridone carboxylic acid derivative, was measured in 20 patients with chronic otitis media. The drug was given orally in a dose of 600mg 3 times a day for one to 24 days (average 6.3 days) on an average of 13.1 hours before the serum and tissue samples were obtained during tympanoplasty. In the 14 patients, for whom data of both serum and tissue concentrations were obtained, the concentrations were 0.90±0.66μg/ml and 3.32±3.50μg/kg, respectively. The tissue concentration was 384±236% times the serum concentration.