The human anterior pituitary exerts about the same effects in the guinea pig as the anterior pituitary glands of rabbit and rat and it differs markedly in its effects from the anterior pit-uitaries of cattle, hog and sheep. This is true especially as far as the effects on ovaries and secondary sex organs are concerned both types of anterior pituitaries produce a stimulation of thyroid and adrenal glands. Injection of extracts of human anterior pituitaries act in about the same way as implantations of pieces of gland tissue.