The relation between non-specific bronchial responsiveness and allergic sensitivity was evaluated in children with asthma. Bronchial responsiveness was determined by methacholine inhalation challenge test, and was expressed as a provocative concentration of methacholine causing a 20% fall in FEV1 (PC20). RAST titre for Dermatophagoides farinae and serum IgE level were evaluated as parameters of allergic sensitivity. When the PC20 vaiues, RAST titres for D. farinae. and serum IgE levels of 47 asthmatic children and 16 normal controls were compared. the asthmatic children had significantly lower PC20 values and higher D. farinae-RAST titres and serum IgE levels than the normal controls. The correlation analyses in 47 asthmatic children have shown that there is no significant correlation between PC20 values and RAST titres for D. farinae (r= 0.04. P > 0.1) or between PC20 values and serum IgE levels (r= < 0.03 P > 0.1). These results suggest thaty although both bronchial hyperresponsiveness and allergic sensitizalion may be in some way related to one another in children with asthma, the magnitude of allergie sensilization does not influence the degree of the non-specific bronchial responsiveness.