Auditory event-related potential (ERP) was studied in idiopathic Parkinson's disease (PD) using our new procedures. We examined 12 non-demented patients with PD, and 9 age-matched control subjects. Ninety responses induced by rare stimulation were continuously recorded from Fz, Cz, Pz referred to linked earlobe electrode (A1A2), and were divided into nine blocks (one block = 10 responses) for statistical analysis. We assessed the habituation of auditory ERP to detect delicate changes related to the information processing in PD. N100 and P300 latencies were significantly longer in PD than in control subjects (p<0.05). P300 latency gradually increased with progression of recording blocks in both PD and control subjects, whereas N100 latency increased only in PD. Three way analysis of variance for P300 amplitude revealed significant effects of subject group, recording electrode site, and trial block. P300 amplitude was smaller in PD than in control subjects. Significant negative correlation between P300 amplitudes and block numbers were observed at Cz and Pz in PD, and at Fz in the control group. Previous reports as well as present results suggest that prolongation of N100 latency might be related to frontal lobe dysfunction, and abnormality of P300 to dysfunction in both the frontal lobe and hippocampus in PD.