Antitumoral interleukin-2 (IL-2) therapy is frequently associated with a neurotoxicity that manifests itself in neuropsychiatric disturbances and, more rarely, with neurological focal signs. With the aim of documenting the involvement of cognitive functions after IL-2 treatment, we studied 20 patients using evoked cognitive potentials (P300) and computer analysis of the EEG signal. A comparison of the tests performed before and after the subcutaneous infusion of IL-2 showed a significant lengthening in mean P300 latencies and a percentage increase in the EEG frequencies contained with the delta and theta bands, especially in the frontal regions.