The luteinizing hormone and thyrotropin-releasing hormones have been shown to be mostly concentrated in the nerve endings of the median eminence. In contrast, the peptidases responsible for their degradation present an ubiquitous localization and most of the reports have dealt with the total soluble activity. A detailed study of the subcellular distribution of these enzymes was thus performed in cerebral cortical and hypothalamic preparations of rat brain. The activity of a soluble marker, lactic dehydrogenase, was also measured to control for possible contaminants. The results showed that only 10% of peptidase activity was present in the nerve ending preparation. Evidence is provided for a non-neglible membrane-bound enzymatic component responsible for TRH degradation at the synaptosomal level of both cortex and hypothalamus.