ACTH 4-10 is a polypeptide which is a fragment of pituitary ACTH and was synthesized by Greven. Studies suggest that it does not have the endocrine or metabolic effects characteristic of ACTH but may have a specific enhancing effect on memory or possibly on attention. Several tasks which emphasized the storage phase of the memory process were presented to young adult (mean age: 23.6 yr) male volunteers. Subjects received 30 mg ACTH 4-10 subcutaneously and their performance on these tasks was compared against placebo. ACTH 4-10 had no effect on unisensory short-term memory. It did, however, impair performance of a bisensory short-term memory task. The bisensory task is complex and requires considerable focussing of attention. It is suggested that ACTH 4-10 may act on the arousal processes which energize behavior unselectively rather than result in focussing of attention.