As A DESCRIPTIVE model, we find it useful to distinguish between vulnerability to schizophrenia which is a relatively permanent, enduring trait, and episodes of schizophrenic disorder that are waxing and waning states. According to this model, episodes of schizophrenia ensue when endogenous and exogenous challengers surpass a threshold set by the individual’s dispositional level of vulnerability. When such challenging events subside, the patient shows at least some degree of recovery, and sometimes even reattains his premorbid level of functioning. However, even when a schizophrenic’s state has normalized, his vulnerability persists and leaves him at risk for future episodes of schizophrenia. The various etiological models of schizophrenia have been presented elsewhere.1 Here it will suffice to suggest that vulnerability to schizophrenia may originate in many ways. Biological models emphasize etiological forces arising from an individual’s internal makeup: his genes, biochemistry, and neurophysiology. Field theory models stress the role of exogenous forces impinging on the maturation, learning and immediate behavior of the individual. The different etiological models often agree in predicting that a particular group of individuals will be vulnerable to schizophrenia, although these predictions are based on different rationales. Most models predict that siblings of schizophrenics represent a group at some risk for schizophrenia, since they share numerous possible sources of vulnerability with the schizophrenic probands. These include a shared gene pool, similar intrauterine environments, common family and community interaction experiences, exposure to the same diseases, die s, physical environments, etc. Because of the evidence that disturbed sensation, perception and attention may be central characteristics of the schizophrenic syndrome,2-4 our selection of potential vulnerability indicators has been influenced by the neurophysiological model of schizophrenia, This model seeks the causes of schizophrenic symptoms in disorders of central nervous system functioning and the capacity to take in and process information. Disturbances of information processing have a prima-facie link with schizophrenic psychopathology because