P300 latency is often delayed in dementia but some authors have questioned its value in clinical practice, because of the relatively low specificity and sensibility of the method. Numerous parameters (latency, duration, amplitude and surface) of N100, N200 and P300 waves were therefore studied in patients with senile dementia, subjects suffering from Parkinson's disease with dementia, and non-demented elderly patients. Using discriminant analysis, more than 90% of the patients were correctly classified. This method could thus be contributory in diagnosing dementia in clinical practice.