The subcellular distributions of the enzymes associated with the methylation and cystathionine-synthesizing portion of the sulfur amino acid metabolic pathway have been determined in the occipital lobe of the rhesus monkey. 5-Methyltetrahydrofolate-homocysteine methyltransferase and 5, 10-methylenetetrahydrofolate reductase activities are located mainly in the soluble compartment. Serine hydroxymethyltransferase activity is located primarily in mitochondria. Cystathionine beta-synthase is a soluble enzyme with a significant component occluded within the nerve endings. Glycine, serine, and cystathionine increase per gram of tissue during development. Glycine and serine are approximately 30% occluded within the nerve endings. These data are consistent with a localization of sulfur amino acid metabolism that supports a differential compartmentation of potential neurotransmitter function and methylation function in the primate.