BACKGROUND: The purpose of the present study was to determine the protective effect of antiasthmatic activity of inhaled heparin, cromolyn sodium, budesonide, furosemide in exercise-induced asthma(EIA). The other important considerable point of this study was the mechanism of bronchoconstriction on EIA. METHOD: Eight subjects with a history of EIA were studied on 5 different experiment days. After obtaining baseline FEV(1) and FVC, subjects performed a standardized exercise challenge. EIA was assessed by measurement of FEV(1) before and after exercise. On experiment day 4, the exercise challengs was performed after the subjects inhaled either heparin (1,000 units/kg/day for 5 days), furosemide (1 mg/kg for 5 days), cromolyn(4 mg/kg for 5 days), or budesonide (400 micrograms/day for 5 days). On experiment day 5, the methacholine brochial provocation test was performed. On experiment day 3, activated partial thromboplastine time(aPTT) was checked. RESULTS: Maximum decrements of FEV(1)(mean+/-SE) among o to 120 minutes after exerise were as follows : heparin was 83.1+/-4.81% (p=0.010), furosemide was 80.5+/-6.87% (p=0.071), cromolyn was 86.8+/-6.53% (p=0.340), and budesonide was 79.4+/-7.31% (p=0.095). Above medications were copmpared to the control value (72.5+/-18.2%) by paired t-test. No medications had effect on PD of methacholine bronchial provocation test. The results were control (1.58+/-0.49 mumol), heparin(4.17+/-1.96 mumol), forosemide (1.85+/-0.86 mumol), cromolyn (2.19+/-0.89 mumol) and budesonide (3.38+/-1.77 mumol), respectively(p>0.05). The inhaled heparin had no effect of anticoagulation. CONCLUSION: These data demonstrate that inhaled heparin has a protective effect on EIA. The effect of inhaled cromolyn was statisitically absent with manufacture's recommended dosage on EIA. So, the dosage of cromolyn should be carefully evaluated in future. Although inhalation of budesonide and furosemide have no statistical significance compared to control, these drugs also have some protective effects on EIA.