Distribution of S-100 protein outside the central nervous system

The distribution of S-100 outside the central nervous system in humans and rats was explored using antiserum to S-100 and the peroxidase anti-peroxidase method of Sternberger. In peripheral nerves the Schwann cells and the outermost part of the myelin sheaths were stained; axons were not. In dorsal root ganglia and ganglia of the autonomic nervous system only satellite cells were stained. In the adrenal medulla a considerable number of cells were stained. In all other organs studied Schwann cells and satellite cells of ganglia were the only elements that were stained. We conclude that S-100 could serve as a marker for Schwann cells in situ.