The effect of quinazolin-4 (3H)-one derivatives with a guanidine substituent was studied: N- [Quinazolin-3 (4H)-yl] acetylguanidine (laboratory code VMA-13-10), N- [2- [4- oxo-3 (4H) -quinazolinyl] propionyl] guanidine (laboratory code VMA-13-15), N- [2- [2-methyl-4-oxo-3 (4H) -quinazolinyl] acetyl] guanidine (laboratory code VMA -13-16) and N- [2- [6-bromo-4-oxo-3 (4H) -quinazolinyl] acetyl] guanidine (laboratory code VMA-13-17) on the morphofunctional characteristics of peritoneal macrophages of white outbred mice under in vitro. The study is carried out on a primary culture of macrophages isolated from the peritoneal cavity of experimental animals. During a 2-hour exposure to the substances under study, their effect on the following indicators was studied: adhesive and plastic properties of macrophages, lysosomal and phagocytic activity. As a result of the studies, it was found that the most pronounced changes in the morphofunctional properties of peritoneal macrophages in experimental animals were observed when exposed to compounds under laboratory codes VMA-13-15 and VMA-13-17, manifested in an increase in lysosomal and phagocytic activity, without a significant effect on their adhesive and plastic properties, which makes these compounds promising for further in-depth study of their immunotropic properties.