Résumé : Immunologic variables in dogs with eosinophilic bronchopneumopathy (EBP) have not been extensively evaluated. The aim of this study was to determine immunoglobulin (Ig) concentrations and to perform phenotypic subtyping of lymphocytes in the bronchoalveolar lavage fluid (BALF) and peripheral blood (PB) of 12 dogs with EBP at the time of diagnosis (TD) and to compare these data with those obtained in healthy dogs, as well as in EBP dogs after antibiotic therapy (TAB) and during corticosteroid treatment (TM). Matched samples of serum and BALF were used to determine Ig concentrations (IgG, IgM, and IgA) by capture enzyme-linked immunosorbent assay (ELISA), from which a secretory index (SI) was calculated. Lymphocyte subpopulations were studied in the BALF and PB by flow cytometry. Log values of BALF IgM and IgA were significantly higher (0.64+/-0.05 and 1.06+/-0.13, respectively) in EBP dogs at TD than in controls and then tended to decrease at TM (0.55+/-0.03 and 1.02+/-0.17, respectively). A calculated SI for IgA was not significantly increased. In the BALF of dogs with EBg the CD4: CD8 was significantly (P < .05) higher (22.6+/-30.3) than in controls (3.2+/-1.9), due to significantly higher CD4+ T cells and lower CD8+ T cells. At TM, the BALF T-cell percentages returned to normal (2.4+/-0.6). We propose that the influx of eosinophils into the airway of dogs with EBP is at least in part mediated by cytokines derived from CD4+ T cells. Further studies of canine cytokines and chemokines will help determine whether canine EBP involves type I hypersensitivity mechanisms regulated by Th2 lymphocytes.