The effects of testosterone propionate (TP) and of 17\g=a\-ethyl-19 nor-testo\x=req-\ sterone (ENT) on the submandibular glands, levator ani muscles and seminal vesicles of castrated mice have been compared. ENT restores submandibular weight and histology about as well as TP but has less effect on the levator ani muscle and much less effect on the seminal vesicles.Both steroids can act directly on the submandibular gland. It is suggested that the effect on the gland may be an indication of the 'anabolic' rather than the 'androgenic' potency of the steroids, and the possible use of this response for the assay of 'anabolic' steroids is discussed.A sexual dimorphism of the submandibular glands of mice was reported by Lacassagne (1940 a, b), and subsequent work has indicated that testosterone is in part responsible for the greater size and the more prominent development of the con¬ voluted granular tubules (serous tubules) of the male gland. Castration results in atrophy of the gland due to regression of the tubules but quite similar histological changes are produced by thyroidectomy. The effects of hypophysectomy are more completely reversed by the administration of thyroxine and testosterone together than by either alone (Grad & Leblond, 1949;Shafer & Muhler, 1960; Burgen & Emmelin, 1961). The changes produced by testosterone have been referred to as a ' masculinization ' of the gland, and it has been claimed that histological changes in the gland are a more sensitive index of androgen secretion than changes in seminal vesicle weight or histological structure (Frantz & Kirschbaum, 1949). In view of the effects of thyroidectomy and thyroxine administration, it seemed that the effect of testosterone might be related more to its metabolic action than to a specific ' mascu¬ linizing ' effect and that it was perhaps unwise to regard submandibular gland changes as a specific and sensitive index of androgen secretion. We have therefore compared the effects on the glands of castrated mice of different doses of testosterone propionate (TP) and 17 oc-ethyl-19 nor-testosterone (ENT). The latter compound is a synthetic steroid said to be as potent as testosterone in anabolic (levator ani) assays but only about one-tenth as potent in androgenic (seminal vesicle and ventral prostate) assays in castrated rats (Saunders & Drill, 1957).