Instracrnial administration of cycloheximide into one hemisphere of the chick brain resulted in inhibition of 14C-leucine incorporation into protein only in that hemisphere when the labelled amino acid was administered intracranially. With pericardial injections of labelled amino acid, inhibition of 14C-leucine incorporation was obtained in both the CXM-treated and the untreated hemisphere, when compared with bilateral saline-treated controls. The levels of inhibition were comparable to those obtained with bilateral administration of CXM. There was, however, a slight but significantly higher level of inhibition in the CXM-treated hemisphere. The results were interpreted as supporting the conclusion that monocular learning in chicks resulted in the formation of an engram only in the trained hemisphere.