The polypeptide ACTH 4-10 has been shown to facilitate learning in animals, and possibly to improve attention and memory in normal human subjects. The purpose of this study was to assess the effects of ACTH 4-10 in cognitively impaired elderly subjects. In a double blind, cross over design, 24 cognitively impaired geriatric outpatients (mean age=71.4, 12 with mild and 12 with severe impairment) received injections of 30 mg or 15 mg ACTH 4-10 or matched placebo on 3 successive days. A cognitive test battery of memory and nonmemory tests was administered each day both before and after treatment. The 30 mg dosage produced a slowing of simple visual RT, a nonsignificant improvement trend in verbal associative memory, and significant, severity dependent facilitation or impairment in day later visual memory. The results suggest that the ACTH 4-10 effects on cognitively impaired elderly are dependent on the dosage and on the baseline cognitive level of the subjects.