This study analyzed the relationship between total respiratory resistance (Rrs) measured by forced oscillation technique and FEV1 during histamine provocation test in 31 children between seven and 17 years of age. Rrs was measured at frequencies between 6 (R6) and 26 Hz (R26). (R6-R26)/R26 was used as an index of frequency dependency of Rrs. A positive histamine test was defined as PC20 less than 8 mg/ml. Seventeen subjects had a positive test, and all of these had increases from baseline of R6 greater than 50 percent and (R6-R26)/R26 greater than 0.45. Of the 14 subjects whose PC20 was greater than 8 mg/ml, only two had changes in R6 and (R6-R26)/R26 of this magnitude. These two subjects had changes in FEV1 of 16 and 18 percent. There was a strong linear relationship between the changes in FEV1 and both R6 and (R6-R26)/R26 from baseline to the final value at the end of the test (r = 0.87 and 0.91 respectively). In conclusion, this study demonstrated that the evaluation of airway reactivity by histamine challenge may be done by forced oscillation technique. It is easy to administer and may allow testing of children unable to perform spirometry.