A 48-year-old female was seen at our hospital after having a severe fever of nearly 40 degrees C, for a period of 9 days. She complained of pain in the left side of her chest. An X-ray examination revealed a slight infiltration of the upper and middle lung fields. At this time, it was learned that the women's pet bird had recently died. This case was diagnosed as acute pneumonia due to psittacosis. Therefore the administration of Roxithromycin was started. After a few day her condition improved. During the course of treatment, serum was taken and a throat swab was done. A micro-immunofluorescence (MIF) test was performed to check the serum antibody levels against Chlamydia psittaci. The serum titer rose from 1:8 to 1:256 in 15 days after admission. The final diagnosis was made after positive isolation of C. psittaci by means of the cell culture method.