Radioaerosol inhalation imaging (RII) has been used in radionuclide pulmonary studies for the past 20 years. The method is well accepted for assessing regional ventilation because of its usefulness, easy fabrication and sirnple application system. To evaluate its clinica1 utility in the study of irnpaired regional ventilation in bronchial asthma, we obtained and analysed RIIs in 31 patients (16 women and 15 men; age ranging 21-76 years) with typical bronchial asthma at the Department of Radiology, Kangnam St. Mary's Hospital, Catholic University Wledical colle#ge, from January, 1988 to August, 1989. Scintiscans were obtained with radioaerosol produced by a HARC(Bhabha Atomic Reserch Center, 1nc]ia) nebulizer with 15 mCi of Tc-phytate. The scanning was performed in anterior, posterior and lateral projections foIlowing 5-rninute inhalation of radioaerosol on sitting position. The scans were analyed and correlated with the results of pulmonary function study and the findings of chest radiography. Fifteen patients had concomitant lung perfusio#n image with ' Tc-MAA. Follow-up scans were obtained in 5 patients after bronchodilator therapy. 1 he patients were divided into (1) att.ack type (4 patients), (2) resistant type (5 patients), (3) remittent type (10 patients) and (4) bronchitic type (12 patients). Chest radiography showed hyperinflation, altered pulmonary vascularity, thickening of the bron- chial wall and accentuation of hasal interstiti.al markings in 26 of the 31 patients. Chest radiographs were normal in the remaining 5 patients. Regardless of type, the findings of RII were basically the same, and characterized by the deposition of radioaerosol in the central parts or in the main respiratory air ways along with mottled nonsegmental ventilation defects in the periphery. Peripheral parenchymal defects were more extensive than that of expected findings from clinical symptoms, pulmonary function test and chest radiograph. Rroomstick sign was present in 1.7 patients. The abnorrnality of RII was poorly correlated with perfusion scans. In all 5 patients treated with bronchodilators, follow-up study demonstrated a decrease in the degree of radioaerosol deposition in the central air way with improved ventilation defects. This study indicates that RII is a useful technique for the evaluation of regional ventilation abormality and the effect of treatrnent with bronchodilators in patients with bronchial asthma.