Memory is a complex multi-event procedure which is profoundly influenced by the overall psychological state. It is thus evident that there cannot be a "memory transmitter" and that many neurotransmitter systems are implicated in different parts of the cognitive process. In general, memory effects resulting from manipulation of the catecholamine systems are a reflection of altered arousal. Modification of cholinergic transmission or that of certain neuropeptides such as vasopressin would appear, however, to involve more directly the memory process itself. This article presents a brief overview of the part played by various neurotransmitter systems in cognitive function and suggests a number of research strategies by which new cognition enhancers may be sought.