SUMMARY Three regions of the human pituitary, viz. (1) anterior lobe, (2) posterior lobe, and (3) intermediate zone (areas of 'basophil cell invasion') in the posterior lobe have been separately assayed for 'B' and corticotrophin in four specimens. The anterior lobe gave the highest levels for both hormones, the posterior lobe contained little of either, while the intermediate zone (of 'basophil cell invasion') yielded some corticotrophin but significantly high levels of 'B'. It is suggested that 'B' may be secreted by the δ cells and corticotrophin by the β cells of the human pituitary.