A previous clinical study (7) suggested that a breakdown in the normal selective and inhibitory functions of attention is a primary disorder in schizophrenia. The present investigation attempts to examine experimentally the validity of this general proposition and of other specific hypotheses derived from it. A battery of tests designed to assess the effect of distracting stimuli upon attentive behaviour was applied to matched groups of 20 schizophrenic patients, 20 non-schizophrenic and 20 normal subjects. It proved possible to differentiate the schizophrenic group from the normal and patient control groups by their poor performance on a number of these tests (Figure-Matching, Spot Tracer, Auditory-Visual Distraction, Auditory-Visual Integration, Auditory-Rotor). Although the scores produced on these tests significantly differentiate the schizophrenic group as a whole, there was a wide scatter in the individual performance of the schizophrenic patients. Some of the schizophrenic patients returned scores on the tests which were at least as high as that of the lowest scoring subjects in the non-schizophrenic patient group. Further analysis revealed that this overlapping of individual test scores was mainly due to the marked deficiency of the hebephrenic patients, all of whom performed at a significantly low level. The implications of these findings are discussed and future lines of investigation are considered.