AbstractAppearance, concentration, and distribution of catecholamines (dopamine and norepinephrine) in embryonic and postnatal chick brain regions were studied. The highest amount of DA was found in cerebral hemispheres and increased gradually to adult levels, whereas in other parts of the brain the concentrations of DA fluctuated during the post‐hatch period. The remainder contained the largest amount of NE, whereas the cerebral hemispheres contained relatively small amounts of NE. Relatively high amounts of NE were found in the cerebellum. A single dose of L‐3, 4‐dihydroxyphenylalanine (DOPA) injected into the 3‐day‐old embryo had no significant effect upon the levels of DA and NE either in the embryonic stages or in the postnatal period. In the 7‐day‐old chick, combined treatment of JB‐516 (catron) and L‐DOPA (IP) induced about a 10‐fold and 2‐fold increase of the brain level of DA and NE respectively about 30 min after injection, and these levels decreased rather rapidly within 2 hr. A group of chicks injected with DOPA at the 3‐day‐old embryonic stage and a group injected with saline were exposed one month post‐hatch to three visual discrimination tasks. There was no significant difference in the performan