The synthesis of factors that monitor the expression of the Thy‐l cell surface component by marker‐negative precursor cells requires an intact left cerebral cortex, whereas the activity of sodium diethyldithiocarbamate, an immunopotentiator that increases this synthesis, seems to require an intact right neocortex. These results suggest a role for the cerebral cortex in the coordinated interregulation of lymphocyte subclasses. The finding extends previous information suggesting relationships between the central nervous system and the T‐cell arm of the immune s