Neuropeptides related to adrenocorticotropin (ACTH) are potent regulators of neurobehavioral functions. In humans, ACTH and its behaviorally active fragment ACTH 4–10 have been consistently found to diminish event-related brain potential (ERP) signs of focussing attention. This study aimed at (1) evaluating effects of ACTH 4–10 on ERP indicators of attention in healthy controls after intranasal administration of the peptide. This route of administration has been proposed to provide a more direct access to the brain than the intravenous administration of the peptide, (2) comparing acute effects and effects of a subchronic treatment with ACTH 4–10, and (3) comparing effects of ACTH 4–10 with those of desacetyl-α-MSH (corresponding to ACTH 1–13 amide) which like ACTH 4–10 binds to subgroups of the melanocortin receptor family. Double-blind placebo-controlled experiments were completed in 54 healthy young subjects. ERPs were recorded while the subject performed an auditory selective attention task. Moreover, a modified Stroop interference test including motivational (food, sex) and nonmotivational words was performed. Acute intranasal administration of ACTH 4–10 (1 mg) reduced the processing negativity (PN) of the ERP over frontal and central cortical areas (p < 0.05) indicating diminished focussing of attention. Moreover, on this condition subjects were more prone to interference on the Stroop task especially with motivational words (p < 0.05). Subchronic administration of ACTH 4–10 (1 mg/day over 6 weeks) did not affect PN and Stroop performance. Acute intranasal administration of desacetyl-α-MSH at equimolar doses (1.68 mg) also remained ineffective. However, some measures of Stroop performance appeared to improve after subchronic desacetyl-α-MSH treatment. Results confirm an acute decrease in focussing of attention after ACTH 4–10. These effects of intranasal administration are likely to reflect a direct action of the peptide on respective brain functions. Moreover, they were specific to ACTH 4–10 and were not obtained after equimolar doses of desacetyl-α-MSH, thus excluding a mediation via the known melanocortin receptors.