Abstract: In this study, PCR was adopted in the detection of pneumocystis carinii DNA in serumand sputum of patients with cancer. The results showed that of 29 patients with abnormal respiratoryshas, 16 were positive in serum, and 11 were postive in sputum. All the 14 patients with0ut abnormal resi-patory signs and 20 normal individuals were negative in serum. These results indicate that serum PCR pro-vides a safe, sensitive and specific method in the diagnosis of pneumocystis pneumonia.