Piracetam (PIR), a cyclic GABA derivative, is the prototype of a new class of psychoactive drugs, the nootropic agents, which improve learning acquisition and the retention of the learning as memory. It was proposed that nootropics act on processes essentially involved in information storage, thus facilitating memory. This property can best be investigated by drug administration after the learning trial and assessing subsequent retention performance. The present study was designed to evaluate the effective time period of memory consolidation, induced by piracetam, by assessing the retention of a learned task in two behavioural paradigms, following administration of the drug after learning acquisition. Physostigmine was used as the standard drug because of its well established facilitation of memory storage. PIR (250 and 500 mg/kg, ip) and physostigmine (0.05 mg/kg, ip) were administered in different groups of mice 5 min, 1, 2, 4, 8, 12 and 24 hr after learning acquistion of two passive avoidance tasks and the retention performance was evaluated 3 days later. The results indicate that, while physostigmine induced significant memory consolidation when administered up to 2 hr after learning acquisition, PIR induced retention of learning beyond this period. Thus, the highest effective post-trial interval for the lower and higher dose of the drug was 8 and 12 hr, respectively, in both the test paradigms. The results confirm that nootropics, like piracetam, are capable of memory consolidation, as assessed by retention of learning, even after intervals of 8 to 12 hr between learning and drug treatment.