['Nedocromil sodium has proven to be efficacious in prophylactic and long-term therapy for the treatment of seasonal allergic rhinitis. We examined the speed of onset of intranasal nedocromil sodium (1%) for relief of symptoms due to ragweed allergic rhinitis.', 'In a double-blind, placebo-controlled trial, 104 patients received either nedocromil sodium or placebo four times daily. Patients spent 10 hours per day for 2 consecutive days in Iowa City Park during the peak of ragweed season. Only patients who had significant symptoms during 3 hourly baseline assessments received drug. Symptom scores for stuffy nose, runny nose, itchy nose, and sneezing and global symptom summary scores were recorded at 19 hourly time points during the 2 days. In the evening patients recorded symptom scores for the postexposure period.', 'In comparison with placebo, nedocromil significantly improved rhinitis symptoms as evidenced by lower symptom summary scores within 2 hours (p = 0.016). Further, this reduction in rhinitis symptoms was maintained throughout the 2-day pollen exposure period. After patients left the study site, postexposure symptom summary scores were also significantly lower in patients treated with nedocromil compared with those treated with placebo (p < 0.007).'] Is nedocromil sodium rapidly effective in the therapy of seasonal allergic rhinitis?