['Multiple mediators including prostaglandin D2 and leukotriene B4 have been shown to increase in nasal secretions during the early response to nasal challenge with antigen.', 'Our objective was to investigate the time course of prostanoid and leukotriene B4 release into nasal secretions on both the ipsilateral and contralateral side after a unilateral nasal allergen challenge.', 'We performed a controlled, randomized trial. Six volunteers were challenged unilaterally with antigen or diluent in a randomized order and discs were used to collect nasal secretions from both nostrils at 2 min intervals for 20 min after the challenge. Prostanoids and leukotriene B4 (LTB4) in recovered nasal secretions were measured by combined capillary gas chromatography-negative ion chemical ionization mass spectrometry (GC/MS).', 'Nasal allergen challenge resulted in a significant and immediate increase in symptoms and sneezing. PGD2 was significantly elevated above diluent values (0.6 +/- 0.6 pg) 30 s after removal of the allergen disc (P < 0.05), reached its peak (423.2 +/- 182.4 pg) at 2 min and then slowly decreased. PGD2 also increased on the contralateral side after unilateral allergen challenge, reaching peak values about six times lower than on the ipsilateral side (70.8 +/- 21.7 pg at 6 min). Levels of 9a, 11b-PGF2 after antigen provocation became significantly higher than after diluent (0 +/- 0 pg) on the ipsilateral side at 2 min (17.2 +/- 5.9 pg), and reached peak levels at 4 min (25.1 +/- 8.0 pg). LTB4 also increased significantly on the side of challenge. For the other prostanoids measured (PGF2, PGF2 alpha, TxB2, 6kPGF1 alpha), no significant changes in either ipsilateral or contralateral secretions were observed after allergen challenge.'] Does unilateral nasal allergen challenge lead to bilateral release of prostaglandin D2?