Introduction: Previously reported results of proteomic analysis of fresh frozen tissues of ovine pulmonary adenocarcinoma (OPA) revealed pyruvate kinase 2 (PK2) as one of the proteins displaying over three-fold higher expression in OPA tissues compared with non-neoplastic lung tissues of sheep. The aim of the present experiment was to determine, using immunohistochemistry (IHC), which cells in the lungs of OPA-affected sheep and the non-neoplastic ovine lungs show the pyruvate kinase 2 expression. Materials and Methods: Archival paraffin wax-embedded tissues of lungs of OPA-affected sheep (n = 5), non-neoplastic ovine lungs showing inflammatory lesions (n = 5) and ovine lungs with no visible lesions (n = 5) were subjected to IHC. The immunolabelling was performed using commercial goat polyclonal antibody against pyruvate kinase 2 (PKM2, LifeSpan Biosciences) and a HRP/DAB ‘visualization’ system (Dako). ,Results: IHC analysis revealed moderate pyruvate kinase 2 immunolabelling in the cytoplasm of neoplastic cells in the OPA tissues, as well as in the bronchiolar epithelium in both neoplastic and non-neoplastic lungs. Moderate to strong positive cytoplasmic immunolabelling was observed in lung macrophages and in occasional leucocytes in all tissues with inflammatory infiltrations, including the OPA sections. Discussion: Results of the present study indicate that the overexpression of pyruvate kinase 2 in neoplastic lungs might be associated not only with tumour development, but also with an increased number of leucocytes expressing PK2. Enhanced expression of this enzyme has been reported in human cancer; however, it has been noted that while normal proliferating cells express a tetrameric form, neoplastic cells express mostly a dimeric form of PK2.