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In a number of reports, Gruzelier and Venables have demonstrated that about 50 per cent of the schizophrenic population do not show the skin conductance orienting response (S.C.O.R.), while those that do respond, do not show normal habituation. Zahn (Orienting response in schizophrenics. J. Nerv. Ment. Dis., 162: 195–199, 1976) has questioned the bimodality of the S.C.O.R. in schizophrenia and suggests that responding/nonresponding could well be due to differential effects of phenothiazine medication. In two experiments (with equally medicated patients), in two different hospitals, the present report confirms the finding of a large proportion of nonresponding in schizophrenia but also suggests that both normal and nonhabituation are seen within schizophrenics and normals. Differential pupillary dilation and constriction parameters are seen in responders and nonresponders although both of these patient groups show tachycardia (the most usual effect of phenothiazines) in comparison to the normal group. The results do not fit easily into the differential effect of phenothiazines hypothesis proposed by Zahn.