Thiamine and thiamine mono-, pyro- and triphosphate were found at detectable levels in synaptosomes isolated from whole rat brain. Synaptosomes prepared from whole brain, cerebellum and medulla were also found to contain uridine and inosine mono- and diphosphatases as well as the thiamine pyrophosphate synthetizing and hydrolyzing enzymes, but no thiamine monophosphatase. By isoelectric focusing on thin layer polyacrylamide gel of Triton X-100 homogenates of synaptosomes, thiamine pyrophosphatase activity could be separated into 10 bands with different isoelectric points. The contents of thiamine compounds and enzymes in synaptosomes were generally lower than those found in neuronal cell bodies.