Unilateral eye removal results in an increased delivery of blood-borne glucose, norepinephrine, choline, and tyrosine, but not of proline, to the denervated optic lobes. Administration of reserpine to chicks increases penetrance of norepinephrine into the brain but not of tyrosine, choline, or proline. Selective alterations in the permeability of the blood-brain barrier may represent a mechanism for the modulation of the delivery of critical nutrients to the brain.