The effect of topical glucocorticosteroids on the allergen-induced nasal hyperresponsiveness, with special reference to treatment time, was studied in a double-blind, randomized, placebo-controlled crossover study. Ten patients who previously had shown allergen-induced nasal hyperresponsiveness participated. After pretreatment with either placebo or various periods with topical glucocorticosteroids, they were subjected to an initial challenge with three increasing doses of allergen and were rechallenged after 24 hours with the lowest allergen dose from the previous day. The nasal responses were monitored by means of symptom scores and measurements of N alpha-p-tosyl-L-arginine methyl esterase (TAME) activity in nasal lavages. Five different treatment schedules were used. In the active treatment alternatives, the glucocorticosteroid treatment was started 48, 12 or 2 hours before or 2 hours after the initial allergen challenge. All treatments were continued up to rechallenge on the second day. As the active treatment we used budesonide, 100 micrograms in each nasal cavity every 12 hours. After placebo pretreatment, as expected, there was an increase in nasal symptoms at rechallenge as compared with the initial allergen challenge with the same allergen dose. The mean (+/- SEM) number of sneezes increased from 5.1 +/- 1.7 to 9.5 +/- 2.0 (p less than 0.05), a composite nasal symptoms score increased from 3.3 +/- 0.66 to 4.4 +/- 0.7 (NS), and TAME activity increased from 14.9 +/- 2.83 to 25.3 +/- 0.5 cpm.10(3) (p less than 0.05). Topical glucocorticosteroid treatment abolished this increase in nasal symptoms and TAME activity (p less than 0.05 for all treatment alternatives).(ABSTRACT TRUNCATED AT 250 WORDS)