The purpose of this study was to determine if the interrupter technique, a noninvasive method for measuring airflow resistance, could be used to assess airway obstruction in children. In 107 children (74 with asthma, 12 with cystic fibrosis, and 21 without lung disease) conductance (mostly of airways) measured with the interrupter technique (Gint) was correlated with both forced expiratory volume in 1 second (FEV1) and the forced expired flow rate between 25% and 75% of vital capacity (FEF25-75). In addition, 17 children with significant airway obstruction due to asthma also had airway resistance measured by body plethysmography (R(aw)) before and after treatment. Resistance and conductance measurements made with the interrupter technique were subdivided into inspiratory (Rint-insp, Gint-insp) and expiratory (Rint-exp, Gint-exp) values. In the 107 children, a high degree of linear correlation was found between Gint and FEV1; for Gint-exp, r = 0.77 (P < 0.001), and for Gint-insp, r = 0.76 (P < 0.001). There was also good linear correlation between Gint and FEF25-75; for Gint-exp, r = 0.70 (P < 0.001), and for Gint-insp, r = 0.67 (P < 0.001). In the 17 asthmatic children who were tested before and after treatment of their airway obstruction, Rint correlated highly with R(aw); for Rint-exp, r = 0.91 (P < 0.001), and for Rint-insp, r = 0.83 (P < 0.001). The pre- to post-treatment changes in Rint and R(aw) were similar.(ABSTRACT TRUNCATED AT 250 WORDS)