DL-2-Amino-5-phosphonovaleric acid (50 microM) administered immediately after a visual reminder presented to day-old chickens between 7.5 min and 24 h following a single trial passive avoidance learning task produced transient losses of memory on retention test, an effect not observed in the absence of a reminder or when the reminder was given 48 h post learning. The duration of the transient deficits decreased with increasing interval between training and the reminder trial. The time of onset of memory loss after the reminder trial appeared to increase with increasing interval between the training and the reminder trials. The results suggest that, for a period of at least up to 24 h after passive avoidance training, retrieval of memory may lead to processes which are sensitive to inhibition by the NMDA receptor antagonist AP5, with the duration of sensitivity post retrieval decreasing as the period of memory consolidation increases. The results extend previously reported findings and suggest the possibility that consolidation of a stable memorial representation of a learning experience may take over several days and may entail the concurrent laying down of a stable retrieval mechanism.