Eighteen asymptomatic Artemisia pollen asthma patients with normal pulmonary function were selected for a double-blind trial of oral immunotherapy. Each patient had a positive skin test to Artemisia pollen extract and also a positive bronchial challenge response to the same extract. The patients were randomly assigned to active treatment or placebo group and received intensive oral administration of Artemisia pollen extract over a 50-day course. The nine patients who received the active treatment ingested a cumulative dose of 396,652 PNU and showed a significant decrease in serum-specific IgE antibodies (P less than .05) and a significant reduction in bronchial sensitivity to the same extract (P less than .01). The changes in these two variables correlated well (r = .8787, P less than .01). The nine patients who received the placebo showed no significant changes in serum-specific IgE or bronchial sensitivity to Artemisia pollen extract. Follow-up of two cases with the same extract showed that the reductions in serum-specific IgE as well as bronchial sensitivity induced by oral immunotherapy were maintained for 3 months.