ABSTRACT: BACKGROUND: The aim of the study was to investigate inflammation during the birch pollen season in patients with rhinitis or asthma. METHODS: Subjects with birch pollen asthma (n = 7) or rhinitis (n = 9) and controls (n = 5) were studied before and during pollen seasons. Eosinophils (Eos), eosinophil cationic protein (ECP) and human neutrophil lipocalin were analysed. RESULTS: Allergic asthmatics had a larger decline in FEV1 after inhaling hypertonic saline than patients with rhinitis (median) (-7.0 vs.-0.4%, p = 0.02). The asthmatics had a lower sesonal PEFR than the rhinitis group. The seasonal increase in B-Eos was higher among patients with asthma (+0.17 x 109/L) and rhinitis (+0.27 x 109/L) than among controls (+0.01 x 109/L, p = 0.01). Allergic asthmatics and patients with rhinitis had a larger increase in sputum ECP (+2180 and +310 mug/L) than the controls (-146 mug/L, p = 0.02). No significant differences in inflammatory parameters were found between the two groups of allergic patients. CONCLUSION: Patients with allergic asthma and rhinitis have the same degree of eosinophil inflammation. Despite this, only the asthmatic group experienced an impairment in lung function during the pollen season.