Evidence implicating molecular steps in memory storage is discussed, particularly with reference to molecular specificity and uniqueness and the possible relevance of these steps to other types of long-lasting transformations such as those of development, regeneration, and tumorigenesis. The role of protein kinase C-mediated phosphorylation of identified protein subtrates, such as a 20,000-dalton GTP-binding protein, is described for associative memory of the snail Hermissenda, associative conditioning of the rabbit, and long-term potentiation. Cyclic AMP-mediated phosphorylation during sensitization of the snail Aplysia is also examined.