Sixteen patients with allergic rhinitis were recruited into a double-blind crossover protocol studying the immediate effect of nedocromil sodium (NS) on the pattern of nasal symptoms and secretions after allergen challenge. After pretreatment with placebo or NS, allergen challenge resulted in pruritus, rhinorrhea, nasal congestion, and/or sneezing within 10 minutes in 12 of 16 subjects. Prostaglandin D2 (PGD2), a marker of mast cell degranulation, increased proportionately with symptom scores, remaining above the 95% confidence interval for 120 minutes after both pretreatments. No difference in PGD2 between the NS-treatment and placebo-treatment days was observed. Protein markers extravasated through the vasculature (albumin and IgG) or secreted by mucosal glands (lactoferrin) were assayed. Total protein, albumin, IgG, and lactoferrin all remained greater than 95% confidence interval for 100 minutes after allergen challenge in the placebo-pretreated group and 120 minutes in the NS-pretreated group. Although there appeared to be a trend for lower secretion of PGD2, albumin, and IgG in the NS-treated group, the overall differences did not achieve statistical significance. This protocol revealed that two topical 130 microliter doses of a 1% solution of NS failed to significantly reduce allergen-induced symptoms, PGD2 generation, or secretion of albumin, IgG, or lactoferrin when NS was compared with placebo. The anti-inflammatory and mast cell-stabilizing effects of NS may require more prolonged pretreatment before provocation to be effective.