Objective:To study the role of allergen testing in vitro and tidal flow-volume measurement in infants with asthmatic bronchitis. Methods:Eighty-six infants with asthmatic bronchitis,81 infants with asthma,and 72 with pneumonia were recruited in the study. Inhaled allergen,food allergen,and mite-specific IgE were determined by Pharmacia UniCAP System. The serum eosinophil cationic protein (ECP) and total IgE were measured as well. Tidal breathing flow-volume loops were obtained after sedation of patients. The tidal volume per kilogram(VT/kg),the fraction of tidal volume exhaled at peak tidal expiratory flow (PTEF) to total tidal volume (VPTEF/VE),and the fraction of exhaled time at PTEF to total expiratory time (TPTEF/TE) were measured. Results:Positive findings of inhaled allergen and food allergen,and total IgE level were elevated in both asthmatic bronchitis and asthma groups in comparison with pneumonia group. There were no significant differences in VT/kg,VPTEF/VE,and TPTEF/TE between asthmatic bronchitis group and asthma group. ECP levels were higher in the asthma group than these in the pneumonia group. ECP levels were negative correlation with VPTEF/VE and TPTEF/TE in the asthma group. ECP levels were lower in the asthmatic bronchitis group than these in the asthma group. ECP levels were negative correlation with VPTEF/VE and TPTEF/TE in the asthmatic bronchitis group. Conclusion:The measurement of allergen,serum ECP,and tidal breathing flow-volume loops were helpful for evaluating airway inflammation and airway obstruction in infants with asthmatic bronchitis.