Eosinophils are important effector cells in allergic inflammation described in allergic rhinitis (AR) and allergic bronchial asthma (BA). During the pollen season serum levels of eosinophil cationic protein (ECP) and eosinophil X protein/eosinophil-derived neurotoxin (EPX/EDN) are increased in BA. The aim of the present study was to evaluate the serum levels of ECP and EPC in pollen atopic patients with AR and BA during the winter. 92 patients were studied. They were divided into three groups: I 29 patients with AR, II 51 patients with BA and III 12 healthy subjects. Allergic rhinitis and bronchial asthma were diagnosed by routine clinical tests: clinical history, skin tests, total IgE and specific IgE. In addition ECP and EPX were determined in serum. All patients were asymptomatic, stable and without medical treatment. Methacholine challenge test (MCT) was performed in all patients. MCT were positive in 4 patients of group I and 45 patients of group II. ECP levels (ug/l) were: 21 (I), 24 (II) and 7 (III). EPX levels (ug/l) were 35 (I), 45 (II) and 21 (III). Statistical differences (p < 0.01) were observed both in ECP and EPX levels in patients with MCT positive in relation to patients with MCT negative, and in allergic patients (I and II) in comparison with the healthy subjects (III) (p < 0.01). ECP and EPX serum levels are increased in patients with a positive MCT in the winter, out of the pollen season, when patients are asymptomatic, stable and without treatment. This fact suggests that eosinophils play an important role in the pathogenesis of bronchial asthma.