The mononuclear phagocytic system consists of cells that have a common origin and whose main role is phagocytosis. The cells of this system originate in the bone marrow, circulate in the blood, mature and become active in different tissues. For instance, monocytes, after they have been activated, migrate into different tissues and mature into tissue macrophages whose primary function is the recognition, phagocytosis and destruction of microorganisms, removal of a dead and damaged cells as well various inert substances. Responding to chemical substances from the environment, macrophages also secrete various pro-inflammatory mediators (cytokines, chemokines, complement components, lipid mediators, enzymes, etc.). The importance of macrophages was observed in many acute and chronic diseases as one of the main cellular mediators of ongoing inflammatory reactions, so there is obvious need for a more detailed study of these cells. Peritoneal cavity is a desirable place for their collection due to the presence of a large number of tissue macrophages. This study shows results of the isolation of macrophages from the mouse peritoneal cavity, which includes the total number and viability of isolated peritoneal cells, the quantity of peritoneal macrophages in the collected peritoneal washing, and the yield and purity after the in vitro adhesion of peritoneal macrophages.