In recent years it has been established that patients with AD have a relatively specific loss of cerebral cortical and hippocampal cholinergic nerve terminals. This may be a reflection of degeneration of cholinergic neurons originating in the nucleus basalis of Meynert and septum which project to the cortex and hippocampus, respectively. In view of the long-standing association of cholinergic mechanisms with cognitive processes and the recognition of selective cholinergic deficits in AD, therapeutic attempts to enhance CNS cholinergic function have been undertaken in patients with AD. While only limited success with this strategy has been achieved to date, the use of TRH may offer a novel, yet rational, approach to treating AD. This assumption is predicated on the extensive literature documenting unique, facilitatory interactions of this peptide with cholinergic neurons throughout the neuraxis. Furthermore, the same rationale may account for the recently reported therapeutic benefit of TRH in patients with amyotrophic lateral sclerosis, which like AD, is a disease whose symptoms are manifested through a progressive degeneration of a subpopulation of CNS cholinergic neurons.