Bacterial endotoxin is a powerful activator of inflammatory immune responses. Overactivation of the first-line defense cells (neutrophils, macrophages) and mediators can lead to progressive tissue damage and multi-organ failure.We earlier demonstrated that, the rare earth metal gadolinium chloride (GdCl3) can attenuate the course of experimental septic and anaphylactic shock by inhibiting the phagocytic activity of macrophages. Materials and methods: male CFLP mice (20–25 g, n = 5 per group) were injected i.p. and i.v. with 10 ?g/10 g bacterial endotoxin (E. coli 026:B6 LPS, Difco Lab, Detroit, lot 110273JB) and GdCl3 (Prolabo, France) respectively, in a dose of 1 mg/100 g body weight. Other animals were given combined treatment with bacterial endotoxin and GdCl3. Results: Bacterial endotoxin increased the total cell count at 24, 48 and 72 h, due to neutrophilia at 24 h and, due to increases in the number of macrophages and lymphocytes 48 and 72 h after the treatment, respectively. The intraperitoneal injection of GdCl3 concomitantly with LPS, attenuated the accumulation of neutrophils and macrophages and induced lymphocytosis to ensure a balanced immune response.