Countercurrent immunoelectrophoresis (CIE) with H. influenzal type b(Hib) and Pneumococci Omni antisera was performed on serum and concentrated urine and pleural fluid samples from 100 patients with acute pneumonia in Beijing Children's Hospital. Thirty-one patients were investigated by bacteriologic techniques (blood culture and pleural fluid culture). CIE was positive in 29/100 (29%) of cases of Hib, 13/100 (13%) of cases for pneumococci. Overall, bacterial causes of pneumonia were diagnosed by CIE in 41/100 (41%) cases. Antigens were detected in 5/90 (5.6%) serum samples, in 36/87 (41.5%) concentrated urine samples, and in 1/2 (50%) samples of pleural fluid. Only one Hib strain was found by pleural fluid culture. The contamination rate of bacterial culture in this group was high (5/31 cases, 16.1%). Therefore, traditional bacteriologic techniques are of very limited value for diagnosing pneumonia in Chinese children. The results showed that bacterial pathogen, especially Hib and Pneumococci, are very common and important causes of pediatric pneumonia in China.