Mid-latency and long-latency auditory evoked responses were investigated in 27 patients with cluster headache who had a mean age of 38.7+/-9.7 years and who were free of pain at the time of testing. Twenty-five age-matched healthy persons served as controls. Latencies and amplitudes of corresponding responses (N100, P200, and P300) were measured. The parameters were calculated at Pz for the P300 and Cz electrodes for the N100 and P200. Multiple analysis of variance revealed a significant overall effect of group (P=0.011). P200 amplitude was significantly smaller in cluster headache patients (P=0.0002). No differences were found for N100 or P300. These data suggest a hitherto unrecognized defect in the information processing pathways, in the early attentive phase represented by the P200 component.