In a double-blind, placebo-controlled multicentre study, the antihistamine acrivastine, was used over prolonged periods for the treatment of seasonal allergic rhinitis. After the initial treatment period of 10 days, 8 mg acrivastine three times daily was significantly superior to placebo in controlling the symptoms of sneezing, itchy nose, running nose, watery eyes, itchy eyes and itchy throat. The benefit from acrivastine was also apparent in the second (14 days) and third (28 days) treatment periods, although the difference no longer reached statistical significance. This was probably due to the large proportion of non-responders in the placebo group who withdrew from the study owing to lack of efficacy. The investigators rated symptom control with acrivastine to be 'good' in comparison to 'poor' control with placebo treatment (P = 0.01) for all three periods. There were no significant differences between acrivastine and placebo in the incidence of adverse experiences at the end of each treatment period. Acrivastine is effective and well tolerated over prolonged periods (up to 52 days) for the treatment of seasonal allergic rhinitis.