We examined associations between neural functions (i.e. N2 and P3b), behavioral (dˊ) and demographic indices (i.e. IQ and Chlorpromazine equivalence) for each genotype within samples related to schizophrenia (i.e. patients with schizophrenia and first-degree relatives)and bipolar disorder (i.e. patients with bipolar disorder and first-degree relatives) in order to evaluate the relationship between COMT genotype and P3b amplitude. The gene discussed is COMT; the disease is schizophrenia.