The time course of change in FEV1, bronchial reactivity, and daily measures of asthma control (peak expiratory flow, symptoms, and beta 2-agonist inhaler use) was determined during 6 wk of treatment with inhaled budesonide, 800 micrograms twice a day, and for 2 wk following cessation of treatment in 40 asthmatic subjects in a double-blind, placebo-controlled, parallel group study. Histamine reactivity, expressed as the provocative dose of histamine causing a 20% fall in FEV1 (PD20), was measured at intervals during the 8 wk of the study, with more frequent measurements after the first and last dose of drug to provide a detailed profile of change at the start and end of treatment. The first dose of budesonide caused a small increase in median values of FEV1 (0.2 L) and PD20 (1.0 doubling dose of histamine), which was maximum at 6 h. There was a further increase in FEV1 and PD20 over the 6 wk in the budesonide group relative to placebo, the maximum increases (0.53 L, 3.4 doubling doses of histamine) being recorded 6 h after the last dose on Day 42. Following cessation of treatment, FEV1 and PD20 declined and PD20 returned to placebo values at 1 wk. Median PEF increased by 40 and 30 L/min in the morning and evening, respectively, with budesonide treatment. Symptom scores and beta 2-agonist inhaler use were lower in the budesonide group than the placebo group during treatment but tended to be similar (symptom scores) or higher (beta 2-agonist) in the 2 wk following cessation of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)