The majority of endocrinological procedures reported result in loss of wt. This report deals with the effects of exptl. wt. loss upon the estrual activity of white rats. Complete or partial starvation with loss in wt. resulted in anes-trus in all of 35 animals. Return of estrus is complete when on refeeding the rats regain the lost body wt. During the inanition-anestrus, estrin and follutein injections result in estrus. This means that the starvation anestrus is due to lack of the estrus- and ovary-stimulating hormones, and in this respect resembles the results from hypophysectomy.