The conditioned stimulus pathway in Hermissenda has been used to examine the time-dependent mechanisms of memory consolidation following one-trial conditioning. Here we report an intermediate phase of memory consolidation following one-trial conditioning that requires protein synthesis, but not mRNA synthesis. In conditioned animals, enhanced excitability normally expressed during an intermediate phase of memory was reversed by the protein synthesis inhibitor anisomycin, but not by the mRNA synthesis inhibitor 5, 6-dichloro-1-beta-D-ribobenzimidazole (DRB). Associated with the intermediate phase of memory is an increase in the phosphorylation of a 24-kDa protein. Anisomycin present during the intermediate phase blocked the increased phosphorylation of the 24-kDa phosphoprotein, but did not block the increased phosphorylation of other proteins associated with conditioning or significantly change their baseline phosphorylation. DRB did not reverse enhanced excitability or decrease protein phosphorylation expressed during the intermediate phase of memory formation, but it did reverse enhanced excitability 3.5 h after conditioning. Phosphorylation of the 24-kDa protein may support enhanced excitability during the intermediate phase, in the transition period between short- and long-term memory.