Unilateral E.C.T. applied to the non-dominant hemisphere has been tried by several workers in cases of depressive illness. Although Levy (1968) has pointed out that the evidence is not sufficient to recommend unilateral E.C.T. as a routine procedure, its main advantages over bilateral E.C.T. have been demonstrated as reduction of post-E.C.T. memory disturbances (Zinkin and Birtchnell 1968 and Valentine et al., 1968), and diminution of post-E.C.T. confusion (Halliday et al., 1968). The present investigation studies the effect of unilateral E.C.T. on schizophrenic delusions and hallucinations with a view to testing the hypothesis that the apparent superiority represented by the diminished side-effects with the unilateral technique might be therapeutically disadvantageous where treatment of patients with delusions and hallucinations is concerned. According to this hypothesis memory impairment may be part of the therapeutic mechanism responsible for the disruption of delusions and hallucinations and their ultimate amelioration or disappearance. If this hypothesis is correct patients treated with bilateral E.C.T. should do better than those treated with the unilateral technique.