Exercise-induced bronchoconstriction (EIB) is often used as a measure of bronchial hyperresponsiveness and employed in epidemiological studies. Different tests are used, including free running tests with poor standardization of exercise load. The present study aimed to assess the role of exercise load in relationship to level of EIB.20 asthmatic children, 9-17 years old with a history of EIB, underwent two treadmill test with 85% and 95% exercise load. The children ran with increasing speed for the first 2 min until reaching a heart rate of 85% or 95% of calculated maximum (220-age) and maintained this speed for the last 4 min. Lung function was measured before running, and 0, 3, 6, 10 and 15 min after the run. Borg scale for perceived exertion was employed for children's self-evaluation of exercise load.Peak heart rate, mean Borg score during 85% exercise load was 178.7/13.6 and during 95% was 194.3/18.2 (P or = 10% in FEV1 after 85% exercise load vs. 20 subjects (100%) after 95% exercise load. EIB from the 95% exercise load test had markedly higher correlation with serum ECP (r=0.77, P<0.001).Exercise load is essential for the interpretation of EIB, and strict standardization of exercise tests should be undertaken. The EIB from the high exercise load tests seemed better correlated to inflammatory activity than the low exercise load test.