It was the aim of the study to compare the efficacy and side effects of oral antihistamine and nasal glucocorticoid therapy in seasonal allergic, rhinitis. In a double blind, double-dummy, group-comparative study, 61 adult grass pollen allergic patients were either treated with dexchlorpheniramine maleate sustained release tablets (6 mg b.d.), or with budesonide nasal spray (200 micrograms b.d.). After a 1-week run-in period, treatment was given for 3 weeks in the grass pollen season. Patients treated with budesonide showed significantly less nasal blockage than those who received dexchlorpheniramine (P less than 0.05), but there was no difference in the number of sneezes and nose blowings. Patients treated with budesonide and a larger quantity of antihistamine-vasoconstrictor eye drops (P less than 0.01). Drowsiness occurred in the group that was treated with dexchlorpheniramine, but mainly during the first week of treatment. The side effects caused by the budesonide spray were few and insignificant. The patients' overall assessment of the treatment favoured the glucocorticoid spray (P = 0.06).