When we face the crucial problem of the aetiological basis of the psychoses we have described, there are three main possibilities to be considered. Either they are to be regarded as symptomatic schizophrenias of purely epileptic causation; or they are independent schizophrenias which have appeared in these epileptic subjects coincidentally as the result of pure chance; or they are forms of schizophrenic illness which have arisen in individuals predisposed thereto by the stresses produced by the epilepsy. An investigation of the genetical background is capable of producing evidence which would assist in answering this question. If the first hypothesis is correct, the incidence of schizophrenic psychoses in the relatives of our subjects should be no greater than in the general population. If the second hypothesis is correct, the incidence of schizophrenic psychoses in the relatives should be the same as in the relatives of schizophrenics of the usual kind. If the third hypothesis is correct, we would expect an incidence of schizophrenia in the relatives of our patients which would lie somewhere between these two figures.