SummaryInvestigating the basal metabolism of hyperthyroïd patients, the author noticed high combustion«peaks»above the generally increased metabolic rate. Laboratory experiments seem to indicate that those raises are due to the fact that the tissues of the Grave’s disease patients, too much impregnated with thyroïd hormone, become hypersensitive to adrenalin normally secreted by the sympathetic system usual reflexes.The author followed the therapeutic effect of Vitamin A in 28 cases. Very good results have been observed in light, or moderately severe cases. The sympathetic symptoms are particularly improved and the metabolic«peaks»seem to disappear. Experiments on animals suggest that the Vitamin A mainly presents an anti-sympathetic action by decreasing the tissue sensibility to adrenaline and sympathine.