This study determined if the degree of exercise-induced refractoriness is determined by the degree of exercise-induced bronchoconstriction. In 12 patients with exercise-induced asthma (mean [SEM] age 27 [3] years) we performed 2 pairs of exercise challenges 45 min apart at different work loads on 2 days. Mean (SEM) total respiratory heat loss during low and high work loads was 3.4 (0.2) and 5.1 (0.4) kcal, respectively. After the first and second exercise challenge at low work loads, mean (SEM) SRaw increased by 107 (15) and 73 (16)% (n.s.), as compared to 361 (40) and 98 (25)% at high work loads (p less than 0.005). We found a correlation between the initial airways response and refractoriness (r = 0.58, p less than 0.005) and conclude that the degree of refractoriness after exercise-induced bronchoconstriction is in part dependent on the severity of exercise-induced bronchoconstriction.