The immunopotenciating effects of ethanol extract, butanol fraction and petroleum ether extract of Korean Ginseng on the immunotoxicity of mitomycin C were investigated in mice. A single administration of mitomycin C induced an apparent but relatively transient reduction of spleen weight, hemagglutination titer, Arthus reaction, RFC and natural killer cell activity. Ethanol extract of Ginseng significantly restored spleen weight, HA titer, RFC and natural killer cell activity. Butanol fraction of Ginseng significantly restored HA titer, RFC and natural killer cell activity. Petroleum ether extract of Ginseng very significantly restored spleen weight, Arthus reaction, DTH, RFC and natural killer cell activity.