To explore the expression of heme oxygenase-1 (HO-1) in the peripheral blood mononuclear cells (PBMCs) and its relationship with pulmonary ventilation function in asthmatic patients, 18 asthmatic patients and 18 healthy subjects were selected. HO-1 protein and mRNA levels in PBMCs were measured by immunohistochemical staining and reverse transcription-polymerase chain reaction (RT-PCR), respectively. Blood carbon monoxide Hb (COHb), serum total IgE and pulmonary ventilatory function were observed. Our results showed that the percentage of cells positive for immunohistochemical staining of HO-1 were significantly higher in asthmatic patients (41.72 +/- 7.44) % than that in with healthy subjects (10.45 +/- 4.36) % (P < 0.001) and the optical density of PBMC HO-1 mRNA was higher in asthmatic patients (26.05 +/- 4.14) than that in healthy subjects (10. 82 +/- 4.26) (P < 0.001). The relation analysis showed that PBMC HO-1 protein and mRNA levels had significantly negative relation with FEV1%, PEFR, MEFR50%, respectively (r = -0.51-0.89, P < 0.05-0.001, respectively) and a positive relation with COHb and serum total IgE (r = 0.48-0. 85, 0.05-0.001, respectively). It is concluded that the expression of PBMC HO-1 protein and mRNA increased significantly in asthmatic patients, and HO-1 may play a significant role in the pathogenesis of asthma. The expression of HO-1 may bear a relation with severity of asthma.