The inhibitory effect of salbutamol and formoterol, a new long-acting beta 2-agonist for inhalation, on the late asthmatic reaction (LAR), was studied in 12 patients with allergic asthma. After a single-blind, placebo-treatment control, equipotent bronchodilating doses of inhaled salbutamol (500 micrograms) and formoterol (30 micrograms) were administered 30 minutes before bronchial allergen challenge in a double-blind randomized design. The early asthmatic reaction was completely inhibited by both drugs (p less than 0.01) but not by placebo. The LAR was also significantly inhibited by both drugs (p less than 0.01); formoterol was only slightly, but significantly, more effective than salbutamol (p = 0.04). In contrast to some earlier studies, the present study indicates an inhibitory effect of beta 2-agonists on the LAR.