Behavioural effects of glutamic acid injection into the body cavity were investigated in the land snail Helix lucorum. An injection itself induced some non-coordinated defensive reactions leading to a partial withdrawal into a shell. The defensive tentacle reflex was facilitated probably due to an activation of the tentacle muscles. The defensive reflex of the pneumostome closure changed in different directions depending on the injected dose of glutamic acid. Feeding behaviour was inhibited by a high dose of glutamic acid. The most pronounced inhibition of the feeding behaviour was induced by N-methyl-DL-aspartic acid.