We have investigated the numbers of circulating eosinophils in schizophrenic patients in relation to the hypoglycemia induced by the injection of insulin before, during, and after a routine course of insulin coma therapy. In the period prior to ICT, these patients demonstrate an orderly relation between these 2 indices of function, and this relation is meaningful in the light of the clinical manifestations noted. In the course of ICT there is a loss of the eosinophil-decreasing effect of hypoglycemia in all patients, and in two-thirds of the group there is in addition a considerable eosinophilia. Subsequent to ICT, there is a dissociation between eosinophil numbers and blood sugar level and a very pronounced lack of clinical response in the face of more severe hypoglycemia. The possible significance of these results is discussed.