To study the time-course of exercise-induced bronchoconstriction (EIB) in asthmatics, we have developed a method for continuous measurement of respiratory resistance using the forced oscillation technique during tidal breathing throughout the exercise challenge. Twenty-three out of 38 asthmatics were exercise responders and five of these responders showed an increase in resistance during exercise. The present technique may be clinically applicable in examination of different types of EIB and as a screening test.