The lung cancer is often associated with the development of pleural effusion. Neutrophils are the most numerous population of immune system cells which are an essential component of tumor leukocyte infiltration. These cells are engaged in the development and maintenance of the inflammation. It is indicated that neutrophils support the development of cancer. The aim of the study was the evaluation of neutrophils, regarding their presence and activity in pleural effusions. This was achieved by assessing of molecular structures, which are used by neutrophils in chemotaxis and phagocytosis. 60 pleural effusions and 34 peripheral blood samples received from patients and 15 peripheral blood samples from the control group were analyzed. Expression of CD11a, CD11b, CD11c, CD18 and CD62L molecules with use flow cytometry was evaluated. The concentration of the neutrophil elastase in pleural effusions were measured with use ELISA test. The number of neutrophils in the peripheral blood of patients with pleural effusion was lower than that observed in the control group. Neutrophils present in pleural effusions were characterized by an increased ability to chemotaxis and secrete significant amounts of neutrophil elastase. Neutrophils recruited into the pleura during the formation of the effusion are an essential element of the developing inflammatory reaction in this environment. The presence of neutrophils in pleural effusion may promote its further formation and support the development of cancer.