SummaryIn ten patients with extrinsic asthma the effects of a new oral chromone FPL57787 and placebo were studied in a random double‐blind fashion to assess the effect of FPL57787 in preventing exercise‐induced asthma (EIA). Exercise testing consisted of steady state running on an inclined treadmill for up to 8 min. FPL57787 gave significant protection (P<0.01) compared to placebo from the maximum percentage fall in FEV1, FVC and MMEF after exercise. FPL57787 also produced a small but significant (P<0.01) percentage increase in FEV1, 2 hr after the drug compared to placebo, whereas no significant increase was seen in FVC or in M