Allergen challenge is associated with an increased excretion of urinary leukotriene E4. The source of this increase is unknown, although the lack of effect of inhaled beta-agonists and sodium cromoglycate suggests that airway mast cells may not be involved. We investigated this further using a new and topically potent inhaled glucocorticoid, fluticasone propionate (FP). A group of 10 mild atopic asthmatic subjects (6 males; FEV1 > 60% of predicted; PC20 histamine < or = 8 mg/ml; and on inhaled beta 2-agonists only) were studied before and after a 2-wk period of FP (1,000 micrograms/day) or placebo administered by metered-dose inhalers as two puffs twice per day through a large-volume spacer. Treatments were assigned in a double-blind crossover fashion separated by a 3-wk washout period. The PC20 histamine was measured at the start and end of each treatment when subjects also received a bronchial allergen challenge. Urine was collected for 4 h after allergen challenge for determination of LTE4 using HPLC-RIA, and 2 h later the PC20 histamine measurement was repeated. The 2-wk treatment with FP significantly inhibited both early and late responses to allergen: the maximum % fall in FEV1 during the early (0 to 2 h) and late response (2 to 6 h) was 32.6 +/- 3.4 and 19.6 +/- 5.2, respectively, following placebo versus 19.5 +/- 4.5 and 3.6 +/- 2.6 following FP (both p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)