Event-Related Potentials (ERPs) are a basic, non-invasive method of neurophysiological investigation. They can be used to assess aspects of human cognitive information processing. They also can be used in experiments on higher mammals. The most important and the most studied component of the ERP record is the P3 wave. It consists of two parts, P3a and P3b. There is no doubt that, besides the use in neurophysiological and psychophysiological research, the P3 wave also has clinical importance. Changes in its latency, amplitude and topography are correlated with clinical findings in a wide range of different ailments. The mini-review we present summarises the current state of the P3 wave research in experimental and clinical studies.