This paper focuses on the temporal dimension of memory formation and storage. Is the usual two-fold separation between short-term memory (STM) and long-term memory (LTM) sufficient to encompass all the phenomena of memory? The traditional view is that STM grades into LTM. Evidence for an intermediate-term memory (ITM) has been proposed by some investigators. We have used both rats and chicks to investigate the stages of memory formation. In this paper, the advantages of chicks for this type of research are briefly discussed. Using a paradigm that produces weak training, the retention function for control chicks appears to be made up of four successive components which we have interpreted as representing the memory buffer, STM, ITM, and LTM. In experiments using a variety of kinase inhibitors, we have obtained evidence that ITM and LTM depend on different classes of protein kinase activities. Agents that act on calcium/calmodulin kinase cause amnesia in the ITM range--15 to 30 min post-training. Another class of inhibitors act on one or more of the kinases PKA, PKC, or PKG and cause amnesia by 60 min post-training, so we interpret this group of inhibitors as inhibiting the formation of LTM. However, the three-stage model of memory may be over-simple. For example some agents including [Leu]enkephalin and MK801 cause amnesia 4 or more h after training.(ABSTRACT TRUNCATED AT 250 WORDS)