The aim of the present work was to study the involvement of protein synthesis in the reconsolidation of memory at different periods of time after training. In mice trained in a conditioned reflex freezing model, memory was reactivated by a reminder combined with administration of the protein synthesis inhibitor cycloheximide. The results showed that suppression of protein synthesis on reactivation of memory 3, 6, and 24 h and 14 and 30 days after training impaired acquired conditioned reflex freezing. These data provide evidence that memories retrieved by a reminder require protein-dependent reorganization at both short (3-6 h) and long (14-30 days) periods after training.