Working memory (WM) has three cognitive components, i.e. encoding and retaining of information, and the retrieval of stored expressions. It is accepted that the left frontal slow wave negativity is an indicator of the functions of working memory. This study aims to investigate the encoded functions of working memory through the variations in the amplitude and latency of P300 wave recorded from three separate locations (Fz, Cz and Pz). The study was performed on five healthy subjects with ages varying between 25 and 30 in the Institute of Cognitive Sciences of Bremen University. The task given to the subjects was to define the stimuli by pressing the buttons in their right and left hands. Event-related potentials (ERPs) were elicited from increasing working memory load in three conditions of an n-back task. It was observed that the amplitude of P300 was low in Fz when compared with those in Cz and Pz. Meaningfully significant differences of P300 amplitude were found among locations only in two-back task (Fz: 5.32 +/- 4.93, Cz: 6.55 +/- 5.31, Pz: 9.97 +/- 6.19; p < 0.05). There were no differences for P300 latency in Fz, Pz and Cz locations. It was concluded that P300 amplitude increased in parallel with the increase in load of working memory. (c) 2004 Elsevier B.V All rights reserved.