In this study, we aimed to investigate event-related potential (ERP) changes in panic disorder (PD) and generalised anxiety disorder (GAD) and to determine whether two disorders are different from each other in terms of endogenous potentials. A total of 35 outpatients who fully met DSM-III-R criteria for PD (8 males and 27 females) were included in this study as the PD group. The GAD group consisted of 30 subjects (5 males and 25 females) who met DSM-III-R GAD criteria, The control group consisted of 29 healthy age and sex-matched volunteers (5 males and 24 females) having no history of psychiatric or neurological illness. ERPs were recorded by using auditory "odd-ball two-tone discrimination task" method. It was found that there was significant prolongation in P3 latency in the PD group compared to the GAD and control groups, Our study suggests that there are some disturbances in early information processing in patients with PD but not with GAD. (C) 2001 Elsevier Science Inc. All rights reserved.