Airway hyperreactivity (AHR) was studied with an astograph for 34 sequential hematopoietic stem cell transplantation (HSCT) patients before and after HSCT. The percentage of Dmin positive patients was 25.0% before HSCT and 25.0-57.1% after HSCT, while all normal subjects were negative for Dmin. The mean Dmin of post HSCT patients was 22.7 u in days 501-1000 and 19.3 u after 1001 days, which was significantly lower than the 45.2 u of normal controls. The patients were divided into two groups according to the treatment before HSCT, strongly treated (S, acute leukemia and non-Hodgikin lymphoma) and weakly treated (W, chronic myelogenous leukemia and aplastic anemia) patients. The ratio of Dmin positive patients and mean Dmin in the W group after HSCT (38.9%, 27.8 u), and the S group before and after HSCT (55.6%, 20.5 u and 45.5%, 23.8 u, respectively), were significantly impaired compared with the findings in the normal controls (0%, 45.2 u). The mean sGrs/Grs count was higher in the W group before HSCT than in the other groups (W before and after HSCT, 0.58 and 0.19, respectively; S before and after HSCT, 0.21 and 0.22, respectively). Taken together, AHR was observed in HSCT patients, particularly for patients in the S group. These data indicate that high dose chemo-radiotherapy including conditioning regimen causes AHR. The mechanisms leading to AHR may be infection, inflammation, and remodeling of the airway.