Three familial cases of psittacosis presented with fever and arthralgia. The first case was a 54-year-old man whose chest X ray film showed ground glass appearance in left S6. Ga scintigraphy revealed stronger accumulation in left lower lobe. Bronchoalveolar lavage fluid was examined in 2 of the cases and activated helper T cells were increased in both of the cases. Lung function was studied in all 3 cases in different phases. Their basic lung functions were different, but there was a similar change in courses, i.e. decrease of small airway flow and the increase of RV. These findings suggest that lung lesion of psittacosis may be related to allergic reaction and diffuse lung disease.