Twenty normal, male volunteers were administered a subcutaneous injection of either ACTH/MSH 4-10 or diluent and two weeks later received the alternate injection in a complete crossover, double-blind design with order balanced. Subjects were given a battery of psychological tests, including a continuous performance task (CPT), following each injection. Visual evoked responses were recorded during the CPT. Resting, eyes-closed EEGs were also obtained. ACTH/MSH 4-10 improved attention and in so doing improved visual-motor learning and visual, but not verbal, memory, EEG data were consistant with activation of the diffuse thalamic projection system.