It has been proposed that delusional thinking 'may be on a continuum with, normal behaviour and can be assessed by taking account of, factors such as the client's degree, of belief conviction or the extent of preoccupation with the belief. In the present research a number of -measures were employed to assess theý delusional thinking of people diagnosed as schizophrenic. - Two -interventions were eipployed: (i) a structured verbal challenge, and (ii) a reality test in which the belief was subject to an empirical test. The research offered support for the continuum view of delusional behaviour, and demonstrated that a number of aspects of delusional behaviour, including the degree of conviction with which the belief is held, are open to modification.