Progress in the study of the caudal neurosecretory system of fishes since the time of Enami is discussed. Ultrastructure and physiology of the same system have been elaborated further through these works. The idea of activation of caudal neurosecretory cells by nervous and humoral stimuli as enunciated by Roy (1962) has been largely substantiated in the subsequent years. The recent works also tend to substantiate the observation of Roy (1962) regarding the peptidic nature of the hormone elaborated by the caudal neurosecretory cells.