The relationship between the release of platelet activating factor (PAF), leukotriene C(4)/D(4)/E(E) (LTC(4)/D(4)/E(4)) and prostaglandin D(2) (PGD(2)) from nasal mucosa in vivo was examined in 24 rhinitis patients allergic to the house dust mite (HDM). During a double blind placebo controlled cross-over study 200 mug fluticasone propionate aqueous nasal spray (FPANS) was administered twice daily for two weeks. In response to allergen provocation (100, 1 000, 10 000 Bu/ml) and during the 9.5 h after this challenge the nasal fluid was obtained by washing the nose with saline and the levels of PAF, LTC(4)/D(4)/E(4) and PGD(2), as indicators of mediator release, were measured at the following time-points: baseline (t = - 1/2), allergen provocation with 10 000 Bu/ml (t = 0), 3.5 and 7.5 h (late phase). After allergen provocation the levels of the mediators increased in the nasal fluids of placebo treated patients (x-fold increase to baseline: PAF, 15; LTC(4)/D(4)/E(4), 12; PGD(2), 1.5). In fluids of patients treated with FPANS these levels tended to decrease. At the time of provocation the levels of PAF, LTC(4)/D(4)/E(4) and PGD(2) showed a significant correlation. The results indicate that these mediators can be used as markers of allergic reactions against house dust mites and that fluticasone propionate aqueous nasal spray tended to reduce the release of mediators of inflammation correlated with beneficial effects on clinical symptoms in this type of allergic reactions.