A 52-year-old man was admitted to another hospital with complaints of fever and dyspnea. Chest roentgenogram revealed bilateral widespread infiltrative opacities, and laboratory examinations showed severe hypoxia, hepatic injury and acute renal failure. In addition, hemosputum and eruption appeared, and he was transferred to our department because of the development of multi-organ failure. Moreover, about 2 weeks prior to admission, a budgerigar he had been breeding died. Although the treatment was supportive therapy alone, the abnormal shadow on chest roentgenogram and laboratory findings improved markedly. Thereafter, we made the diagnosis of psittacosis, because the serum titer of a complement fixation test against Chlamydia rose from 1:8 on admission to 1:512 after 2 weeks. On admission, PMN and lymphocyte populations increased in bronchoalveolar lavage fluid (BALF), and 2 weeks later lymphocytes alone increased markedly. Thereafter, we observed lymphocytosis in serial BALF findings for 12 weeks. These findings indicate that lymphocyte alveolitis persisted long after the pneumonia had resolved. Moreover, Ga scintigraphy also revealed accumulation in the filed of shadows which had been absorbed and disappeared on the chest roentgenogram. These results suggest that lymphocytes play a leading role in immune host defenses and that immunological reactivity is prolonged in psittacosis.