The transcription factor cAMP response element (CRE)-binding protein (CREB) plays an essential role in the induction of many forms of long-term synaptic plasticity. Levels of CREB1, the Aplysia homolog of CREB, show sustained elevations for several hours after the induction of long-term synaptic facilitation (LTF). Furthermore, CREB1 binds to the promoter of its own gene. These results suggest the existence of a CREB1-positive feedback loop that contributes to the consolidation of LTF. In the present study, we provide a detailed, quantitative characterization of the dynamics of CREB1 mRNA and protein as well as CREB1 phosphorylation after LTF induction. Injections of CRE oligonucleotides prevented the increase in CREB1 in response to 5-HT, corroborating the existence of the CREB1 feedback loop. This loop probably sustains CRE-dependent gene transcription, which remains elevated for at least 12 h after LTF induction. LTF is blocked by injection of CREB1 antibody after the induction phase, suggesting that the CREB1-positive feedback is required for consolidation of LTF.