Histological and ultrastructural changes of hypophyseal gonadotropic cells of rats which received a 15% solution of ethyl alcohol for 6 months were studied. Light microscopy revealed hyperplasia and hypertrophy of these cells; some contained a vacuole of varying size. Ultrastructural analysis showed that this vacuole originated from, and anastomosed with, dilated cisternae of the granulated endoplasmic reticulum. Vacuolated cells in the pituitary of alcoholized rats were identical with cells observed after surgical or chemical castration. The development of these alcohol-induced castration cells is achieved in four stages.The first stage was characterized by beginning hydropic degeneration and other still reversible alterations. Cells in the second and third stages seemed already irreversibly on their way to decay.The fourth stage was represented by typical signet-ring cells. Our results offer a morphological basis to the adoption of a biphasic effect of alcohol on gonadotropic secretion.