(1) The bioelectric potentials from the brain of the rabbit have been studied during metrazol and insulin shock. Insulin, administered subcutaneously, causes a marked increase in the slow wave activity during the coma stage. Cortical potentials during the convulsions are masked by the potential artefacts caused by the violent movements. Except for a few cases of localized spike potentials recorded from the cortex during the pre-convulsive stage, no characteristic cortical potentials are seen immediately preceding the convulsion.(2) The potentials recorded from the cortex following a shock injection of metrazol may be divided into four phases. These phases are correlated with the various stages of the physical shock.(3) Thalamus, midbrain and cerebellum show abnormal electrical activity during metrazol shock.(4) Sections at various levels in the central nervous system show that the electrical response in the cortex due to the action of metrazol, is not primarily dependent on the severed pathways. Characteristic shock potential sequences may even be recorded from small areas of neurologically isolated cortical tissue. The physical shock, on the other hand, is altered profoundly by these neurological sections.(5) Minute quantities of metrazol, applied locally to discrete areas of the cortex of the rabbit, initiate a bioelectric response which, although much more localized, resembles closely that seen following intravenous injection. This activity may spread to other cortical or even sub-cortical areas, presumably by facilitation.(6) An attempt is made to explain something of the action of metrazol on the brain, on the basis of what is already known regarding the effects of faradic stimulation of the cortex.