Two earlier studies (Venables and Tizard, 1956a, b) on the reaction time (RT) of schizophrenics have shown that as the intensity of a visual stimulus is increased beyond an optimum point, RT to the stimulus increases. This “paradoxical” increase in RT is not shown by normal subjects, whose RT decreases as the intensity of visual stimulus increases. It was also found that the paradoxical phenomenon with visual stimuli was only shown on an initial occasion of testing. When the experiment was repeated twenty-four hours later, although there was no alteration in the mean level of RT, the pattern of increase in RT with increasing intensity, previously found, was absent.