The plethora of reports on lateralization and psychopathology is part of the Zeitgeist that spawned ' neuroscience', and in psychology the concern with brain behaviour relations. The underpinning of abnormal behaviour with a disturbance in lateralization has long been a source of speculation (Zangwill, 1960) and more recently gained impetus from the association of schizophreniform psychoses with left-sided temporal lobe dysfunction and affective psychoses with a corresponding right hemisphere disturbance (Flor-Henry, 1969. After a decade of intensive research what can be concluded ?For those who acknowledge terra firma when morphological deficits are proven, Luchins et al. (1979) found with computer tomography that normally occurring lateral asymmetries in the width of frontal and occipital lobes were reversed more often in schizophrenia than in controls. The coincidence between the two asymmetries was not given, but frontal asymmetries were reversed in 13 % of controls and 33 % of patients, with 9 % and 25 % the corresponding percentages for occipital reversals. If reversals of function follow, they may confound comparisons between patients and controls so that in schizophrenia, and to a lesser extent in controls, group distributions of laterality scores will show asymmetries in both directions.This serves to introduce the complex methodological problems that laterality research faces. One may construe a lateralized disorder in patients not only if the normal asymmetry is absent, or reversed, but also in the presence of the normal asymmetry, provided that performance is reduced below the level of controls. It is essential, therefore, to equate the patient and comparison groups for task difficulty. Nevertheless, quite apart from the results of Luchins et al., it is not entirely satisfactory that all three possible outcomes may be considered evidence of a lateralized deficit to a single hemisphere.Fortunately, not all approaches are prone to this qualification. If a deficit is defined in terms of the nature of the psychological processing measured, instead of laterality, a conclusion may run that verbal processing compared with spatial processing was deficient, in which case the question ' to which hemisphere do verbal functions belong?' is of secondary importance. With this strategy an experiment should include tasks specific to each hemisphere which in themselves are of equal difficulty. When such requirements are met they also circumvent a major criticism that bedevils psychological studies: namely, the intrusion of factors such as motivation, test anxiety, institutionalism, etc.; such issues will usually affect both hemispheres, and the nature of a lateralized deficit is likely to be neurophysiological. Furthermore, as a global hemispheric deficit is not an issue in current theories, a matter sometimes overlooked, the tests specific to each hemisphere should possess a neuro-anatomical equivalence. This requirement is more easily met when measuring the earlier stages of processing or in tasks processed by eith...