PURPOSE: This study was performed to evaluate the polymerase chain reaction (PCR) in the diagnosis of Mycoplasma pneumoniae pneumonia in comparison with the specific antibody test. METHODS: Five hundred and ten patients with pneumonia, ranging from the ages of 8 months to 15 years who were admitted in Sung-Ae and Kwangmyung Sung-Ae general hospitals from Nov. 1996 to Oct. 1997, were enrolled in this study. Specific antibody test of the serum using Serodia Myco II kit and PCR of the sputum or throat swab were performed on admission simultaneously, and follow-up antibody test was done during the convalescent stage if they showed sero-negative at first. Among the PCR positive patients, 40 were treated with erythromycin initially, and were followed with PCR on the 7th day of treatment. RESULTS: The sensitivity of PCR to the specific antibody test was 82.5%, and the specificity, 98.4%. The false positive and negative rates of PCR to the specific antibody test were 1.6% and 17.5%, respectively. Fifty-six (91.8%) of the 61 patients who showed sero-negative and PCR positive on admission were determined as sero-positive at the convalescent stage. Negative conversion of PCR at the convalescent stage was noted for 32 (80%) of 40 patients who were treated with erythromycin. CONCLUSION: The PCR was considered to be valuable due to its high sensitivity and specificity as a diagnostic method of Mycoplasma pneumoniae pneumonia. The effect of the method was more apparent than the specific antibody test in early diagnosis which is clinically important. In addition, it seems to be more useful in the appreciation of treatment and epidemiologic study than the culture method that shows low sensitivity and takes too much time.