Auditory Event-Related Potentials (AERP) were elicited in 25 beta-thalassemic patients, three days before and three days after a blood transfusion. The amplitude, latency and topographic distribution of P300 (P3) as well as N1, P2, N2 components were measured for the two assessment times. No significant differences in either amplitude, latency or topography were observed between the two situations, but thalassemic patients had significantly prolonged P3 latencies comparing to controls though none of them exceeded 3 standard deviations of the control mean values. Regarding P3 topography, 10 out of 25 patients showed a right centroparietal distribution area. It is concluded that information processing, as far as it is reflected in AERP components is impaired in thalassemic patients and blood transfusion have no significant influence in cognitive functions.