114 castrate, virgin [female] mice received subcut. injs. of ant. pituitary material obtained from pregnant cattle. Dosages ranged from 50-200 mg. per mouse while inj. periods varied from 4-8 days. 57 mice showed lobule development of the mammary glands equivalent to those of mice pregnant from 4-8 days. 46 castrate [female] mice received subcut. injs. of an ether soluble extract of cattle AP which required 0.23 mg. for a mouse unit of the duct growth factor. The inj. dosages varied from 0.25-39.2 mg. during periods ranging from 6-30 days. Autopsy revealed only 2 cases of lobule development. These positive results could not be duplicated on retrial. Both the mammogenic duct growth and the lobule-alveolar growth factors are present in the fresh AP tissue of pregnant cattle. The mammogenic lobule-alveolar growth factor is apparently not associated with ether soluble duct growth extracts of the AP at least as observed in expts. on the mouse.