Experiments were performed to investigate effects of ethanol and saccharin on the immune system in rats. 4% ethanol and 0.02, 0.20, 2.00% saccharin solution in 4% ethanol were provided ad libitum by tap water for 4 weeks. Rats were sensitized and challenged with sheep red blood cells (S-RBC). Immune responses were evaluated by relative immuno organ weight, antibody production, Arthus reaction, delayed type hypersensitivity, and rosette forming cell. Ethanol exposure decreased thymus weight and delayed type hypersensitivity. A combined solution of ethanol and saccharin decreased water intake, growth rate, spleen weight, thymus weight, humoral and cellular immune response. Especially, a 2% saccharin solution in 4% ethanol very significantly suppressed cellular immunity.