Chlamydia pneumoniae was isolated from the pharyngeal swab of a 15-year-old patient with acute bronchitis. The serum IgM antibody against C.pneumoniae was elevated up to 160-fold in the acute phase and decreased to 20-fold in the convalescent phase using the microimmuno-fluorescence (MIF) test. IgG antibody titers in the acute phase and the convalescent phase were 40-fold and .160-fold respectively using the MIF test. The patient recovered from the bronchitis without any effective treatment, indicating spontaneous cure of the disease.