A placebo-controlled double-blind randomized trial was carried out to assess the efficacy of pseudoephedrine in relieving nasal congestion in the common cold. Fifty-four previously healthy persons who had a common cold for at least 5 days or less at the start of the study with moderate to severe nasal congestion were recruited, 52 completed the trial. Following a single dose of oral pseudoephedrine (60 mg capsule) or placebo, symptoms of congestion improved significantly compared with placebo at times 60, 90, 120, and 150 min after the dose. Total nasal minimum cross-sectional area and nasal volume measured by acoustic rhinometry increased significantly compared to placebo (P = 0.018 and P = 0.003, respectively) after the dose. There was no significant change in nasal area as measured by active posterior rhinomanometry after pseudoephedrine compared to placebo. We conclude that in the acute common cold, a single 60 mg dose of pseudoephedrine produces significant increases in the dimensions of the nasal cavity compared to placebo and this is associated with a reduction in the symptom of congestion.