This study was carried out to determine the concentrations of eosinophil cationic protein (ECP) and tryptase in the nasal lavage fluid (NLF) of 24 children (C) with grass pollen rhinitis as well as rhinitis symptoms before and after nasal provocation tests with or without a levocabastine (anti-H1 topical antihistamine) pretreatment. All C were monosensitized to grasses only. Twelve patients (Active Group = AG) were tested with a nasal provocation test with grass pollen (NPT) carried out by the insufflation of increasingly higher doses of an allergenic extract powder, while the other 12 patients (Placebo Group = PG) underwent just a nasal provocation test with lactose (placebo) (NPTp). The prechallenge NLF, obtained both before (C) and after (AG) levocabastine pretreatment, was compared to that obtained after periods of 2 and 24 hours postchallenge. In the AG, before and after levocabastine pretreatment, the tryptase concentrations had not significantly increased, whereas the ECP concentrations were found to be significantly higher (p < 0.05) in just the 24-hour postchallenge samples. In the PG the rhinitis symptoms were not induced by the NPTp and there was no significant change in either ECP or tryptase concentrations. In the AG a levocabastine pretreatment induced a significant increase (p < 0.05) in the cumulative allergen doses administered by the NPT. There was a reduction of the nasal symptoms in 7 patients, while in 3 subjects there was only a slight improvement, but in 2 subjects no effect was encountered. In conclusion this study shows that a levocabastine pretreatment before an NPT in patients with grass pollen rhinitis, outside the grass pollen season, induces a significant increase in the cumulative allergen doses (administered by the NPT) which provoked rhinitis symptoms but is not able to demonstrate any significant reduction in the ECP concentrations of the NLF.