The clinical potency of budesonide, a new glucocorticosteroid, was compared in a randomized double-blind study with beclomethasone dipropionate in the treatment of seasonal allergic rhinitis during the ragweed-pollen season. Sixty-one subjects were matched according to their skin sensitivity to ragweed-pollen extract and the severity of ragweed-induced rhinitis during the previous season. Thirty subjects received budesonide, and 31 received beclomethasone dipropionate, 50 micrograms per actuation. A double-dummy technique was used to achieve blinding, since the aerosol canisters and adaptors were dissimilar. Subjects were instructed to keep rhinitis well controlled by starting intranasal trial medication as soon as symptoms became troublesome, two puffs into each nostril, when it was needed, up to four times per day. If this became inadequate, subjects received supplementary chlorpheniramine maleate, 4 mg. Nasal symptoms (none = 0, mild = 1, moderate = 2, and severe = 3) and all medication use were recorded daily in a diary. Budesonide demonstrated better clinical potency than beclomethasone in that less was needed to maintain good control of nasal symptoms. Side effects were mild and transient for both groups.