In order to elucidate the important factors for refractoriness following repeated exercise in exercise-induced asthma(EIA), we investigated the relationship between the change of bronchial hyper-reactivity to methacholine during the refractory period and the degree of refractoriness following the exercise.

Ten EIA patients were tested. First visit included methacholine bronchial provo-cation test(MBPT) followed by exercise 1 and repeated MBPT separated by a 60 min. On seco-nd visit, exercise 3 were repeated after 60 min of exercise 2, and refractoriness was measured.

The maximal broncial constriction measured by FEV1 was 22.6±4.2% and this reaction was recovered over 95% within 60 min. Methacholine PC20(PC20M) was decreased after exercise in six from 10 EIA patients. There was no significant relationship between the degree of exercise induced bronchial-constriction and the chagne of PC20 after exercise. The bronchial hyper-reactivity to methacholine was in--creased after exercise even with the refracto-riness in some of EIA patients.

Refractoriness followed by repeated exercise does not seem to be due to the decreased bronchial hyper-reactivity.