1. Recent evidence suggests that treatments given after training may influence memory in two ways: by becoming themselves incorporated to the experience, or by altering post-training mechanisms involved in the storage of the experience. The two processes may be called consolidation. 2. Some endogenous substances that are normally released during or after training (brain beta-endorphin; the peripheral stress hormones, ACTH, epinephrine and vasopressin) appear to be of particular importance. Their effect may become incorporated to the experiences as a conditioned stimulus (CS), generating state dependency. The effect of beta-endorphin appears to be physiological, since the substance is released by novel experiences. 3. Post-event information provided by other training experiences, in rats, or by comments or leading words, in humans, may also incorporate to the experiences, altering their content qualitatively or quantitatively. 4. A variety of substances including the stress hormones at low doses and analeptic drugs may facilitate retention when given after training. In this case, the effect is best explained by an enhancement of the post-training strengthening of memory traces. 5. The reiteration of part of the experiences at the time of testing facilitates retrieval. This may be viewed as a reconstruction of consolidation at the time of retrieval, and may be obtained using cognitive material ("priming"), or neurohumoral stimuli (a beta-endorphin injection, or a presumable release of brain beta-endorphin by an interpolated novel experience). The effect can be seen in animals rendered amnestic by electroconvulsive shock, and in humans with amnesia of organic and non-organic nature. 6. The human amnesic syndrome seems, thus, largely explainable by a deficit of retrieval. It is possible that the stimulation of retrieval by priming, or by drugs, through the "reconstruction" of consolidation, may be useful for the relief or treatment of the human amnesic syndrome.