Clinical studies of cognitive effects of ACTH fragments carried out so far with ACTH (1-10) and (4-9) (Org. 2766) brought about inconsistent and partly disappointing results. Efficacy could not be demonstrated in patients with Alzheimer's disease (AD). A possible reason for these results is the low metabolic stability and low lipophilicity of these compounds. HOE 427 has a considerably prolonged metabolic stability, has a high lipophilicity, and is much more potent than are existing compounds in pharmacologic models of memory and learning. It also was proven to have significant effects on ACh metabolism. Single dose studies in groups of mildly cognitively impaired elderly subjects and in patients with AD showed slight but significant effects on attention and mood. The effects were less consistent in patients than in healthy subjects.