A study on the nasopharyngeal carriage and antimicrobial susceptibility of Haemophilus influenza among children was conducted in Beijing Children's Hospital from April to May 2000. The study included 292 children between I and 60 mo of age with acute upper respiratory tract infection. Nasopharyngeal swabs from these patients were cultured, and 105 Haemophilus influenzae strains were isolated, 3 of which were type b. Antibiotic susceptibility of the strains was determined using disk diffusion and E-tests and the results compared with those of isolates from children with pneumonia in 1999. The carriage rate of Haemophilus influenza was 36.0% (105/292). It was found that 4.8% and 1.0% of isolates were resistant to ampicillin and cefaclor, respectively, and 5.7%, 16.2% and 77.1% were resistant to chloramphenicol, tetracycline, and sulphamethoxazole/trimethoprim, respectively. Amoxicillin/clavulanic acid, cefuroxime, ceftriaxone, azithromycin, and clarithromycin were uniformly active to all strains. Compared with the data from 1999, there was a significant increase in resistance to tetracycline (from 12.7% in 1999 to 16.2%) and sulphamethoxazole/trimethoprim (from 40.5% in 1999 to 77.1%). Conclusion: H. influenzae isolates from outpatients in Beijing Children's Hospital had low ampicillin resistance and were sensitive to amoxicillin/clavulanic acid. Sulphamethoxazole/trimethoprim resistance rates increased rapidly compared with those in the 1999 data. Further surveillance investigations are important for the choice of empiric therapy of acute respiratory tract infection.