In a previous study it was shown that the acetyl moiety can be incorporated into the protein of purified synaptosomes (1). This process was inhibited by veratridine and the inhibitory effect was counteracted by tetrodotoxin. This suggested that the flux of Na+ may be related to the acetylation process. We now report that in a sodium free medium the amount of acetylation is increased and the inhibitory effect of veratridine (veratrine) is no longer evident. The addition of Na+ leads to a decrease in acetylation in the presence of veratrine. The presence of scorpion toxin has an effect similar to that of veratrine and the two are not additive. Hence, they appear to act on a common site. Molecular sieve chromatography shows four radioactively labeled peaks, two of which are particularly affected by veratrine. We also show that [3H]acetate incorporated into synaptosomal protein can be recovered as acetyldansylhydrazide. In addition, the concentration of free and bound acetate was measured in whole brain as well as in synaptosomes.