Terfenadine (60 mg b.i.d.) was compared with placebo in a randomized, double-blind, cross-over study in twenty-three patients with birch pollen allergy. The patients were treated during two 7-day periods separated by a 2-week wash-out period during a season free from birch pollen. Nasal provocations with birch pollen extracts were made at study entry and after each treatment period. Blockage (rhinomanometry), secretion (weight) and sneezings (number) were compared between treatments. The results showed a significant inhibitory effect of terfenadine on secretion and sneezing, but no significant difference between treatments with regard to blockage. Terfenadine showed no signs of sedative properties or inhibition of salivation.