Effects of zinc chloride (Zn) on the immune responses of lipopolysaccharide (LPS) were studied by using ICR mice. Mice were divided into 4 groups (10 mice/group), and Zn was given to the mice with i.p. injection at 0.3 mg/kg 5 times a week for 14 days, and 1 hr after Zn administration, LPS was given with i.p. injection at 5 mg/kg twice a week. Mice were immunized and challenged with sheep red blood cells (SRBC). Immunobiological responses were evaluated by humoral, cellular and nonspecific immunity. LPS treatment significantly increased the relative weights of spleen and thymus, hemagglutination titer (HA) and proliferation of splenocytes compared with those in controls, but significantly decreased the body weight gain. Zn treatment significantly increased proliferation of splenocytes and circulating leukocytes compared with those in controls. Combination of Zn and LPS significantly decreased the body weight gain and proliferation of splenocytes compared with those in controls. Combination of Zn and LPS significantly decreased HA and proliferation of splenocytes than in LPS alone. These findings indicate that zinc lowered the humoral immune responses of LPS.