The effect of an immunostimulator, Freund's complete adjuvant (FCA). on the ability of Wistar rats to learn in a visual discrimination test was studied by food-getting and electric-shock avoidance methods. A significant improvement in learning ability was demonstrated under the influence of FCA when the negative reinforcement method was used, but a worsening when the positive reinforcement method was used. Analysis of the dynamics of extinction of the reflexes formed gave similar results. The possible relations between immunogenesis and memory forming processes are discussed.