1. Excitatory amino acids are major transmitters within the CNS. 2. Postsynaptic receptors for these transmitters, particularly those of the NMDA subtype are important in a variety of physiological and pathological processes. Therefore psychoactive drugs and potentially therapeutic drugs may target these receptors. 3. NMDA receptors can be regulated by competitive antagonists or by dissociative anaesthetics which act as use dependent blockers of the NMDA channel. 4. Alternatively drugs could modify intracellular second messenger systems that control expression of NMDA receptors.