This study evaluated the relative contributions of vascular engorgement and less reversible components of inflammation (edema, cellular infiltration) to production of allergic nasal congestion. We established the minimum nasal airway resistance (NAR) inducible by oxymetazoline spray in 29 asymptomatic patients. During ragweed season, we restudied them with the same decongestant regimen before and after 1 week of treatment with oral methylprednisolone (Medrol tablets, Upjohn) or a matched placebo. It was not possible, in the conditions of this study, to decongest symptomatic patients to baseline using only the topical vasoconstrictor. This could be accomplished in those receiving methylprednisolone. Corticoid therapy relieved a non-vascular component of congestion or rendered vasoconstrictor therapy more effective.