1. Proteins of different regions of the Hirudo medicinalis central nervous system have been analyzed by means of two-dimensional electrophoresis. 2. Subcellular distribution of phosphoproteins has been studied in leech segmental ganglia. 3. Phorbol 12,13-dibutyrate, a protein kinase C activator, stimulates the phosphorylation of a number of proteins whose isoelectric points and mol. wts are presented. 4. Putative roles for these phosphoproteins are discussed.