A considerable number of experiments, reported since 1965, has been concerned with cerebral hemisphere differences and the processing of tachistoscopic visual information. The present paper critically examines the findings from laboratory experiments with normal Ss and from clinical experiments with brain-damaged patients. Three general conclusions are reached from this analysis: (1) Much of the available evidence on tachistoscopic laterality differences and hemispheric asymmetries is ambiguous, equivocal, and inconsistent; this is attributable to inadequate methodological considerations and misinterpretations of response indicators. (2) The reliable evidence suggests the hemispheres differ in efficiency to initiate specific responses and in ability to analyse/encode visual information. (3) Future research into hemispheric determinants should supplement traditional recognition-accuracy indicators with non-vocal, non-identificatory measures in order to separate response-initiation from visual-analysis effects.