The afferent humoral system exerts significant influences on brain activity. Central nervous actions of the adrenocorticotropic hormone (ACTH) are most likely to be mediated by information coded in a portion of this hormone structure corresponding to ACTH 4-10. Our previous research suggested an impairing effect of ACTH 4-10 on electrophysiological signs of selective attention in humans. The present experiments in 12 male subjects investigated the influences of ACTH 4-10 on different aspects of attention as indicated by auditory event-related potential (AERP) components. Furthermore, dose-response characteristics of these influences should be examined. Attention performance was tested in a dichotic listening paradigm, after 0, 0.1, 1.0, and 10 mg ACTH 4-10, administered intravenously 1 h prior to testing according to a double-blind latin-square design. Different aspects of attention were measured by brain electrical responses evoked either by frequent standard or rare target tone pips, which the subject had to attend to, or to ignore. The selective type of attention was reflected by the Nd determined as mean difference in amplitude between AERPs to tone pips when attended and when unattended, for a latency range between 0-460 ms post-stimulus. In addition, plasma cortisol, heart rate, blood pressure, and behavioral performance were measured. Results indicated a clear reduction of the Nd amplitude after all doses of ACTH 4-10. Other indicators of attention mechanisms such as mismatch processing were not affected by the peptide. The diminished Nd after ACTH 4-10 was due to an increased processing of unattended stimuli, but simultaneously attended tones were processed less intensively.(ABSTRACT TRUNCATED AT 250 WORDS)