Neurotoxicity induced by interferon (IFN) is revealed by neurobehavioral changes, such as irritability, somnolence, lack of motivation, and delayed ideation. As these side effects persist throughout IFN-alpha treatment, we studied cerebral mapped auditory evoked potentials (MAEP) in 20 hepatitis C virus antibody (HCV Ab)-positive chronic active hepatitis patients before and after administration of leukocyte IFN-alpha (i.m. 3,000,000 IU). Some of the main components of MAEP, such as morphology, latency, and power spectra, were altered before IFN injection. These parameters changed 7 h after administration as revealed by increased quality and quantity of acoustic signal reaching the brain cortex and appearance of physiologic waves in patients with mild/intermediate liver disease. These effects revealed 48 h after IFN administration.