In patients with frontal lobe tumours the averaged visual evoked responses (AVER) and their dispersion pattern (DP) in visual areas were investigated before and at different periods after operation. Important changes in AVER (in amplitude and latency) were found in the patients with tumours on the midline or in one of the frontal lobes. The DP was abnormal in all the cases. There was no relation to visual acuity, tumour location and existence of intracranial hypertension. After operation, despite the clinical improvement, the alterations of AVERs or DPs were very marked and in some cases became even more important than before. The role of the frontal lobe in the organization of the responses to peripheral stimuli in the visual areas is discussed.