Evidence is presented for antigenicity of TSH, ACTH, and growth hormone. Rabbit antisera to these hormones were prepared and then tested by means of a hemagglutination test in which antigen is coupled to red blood cells, by means of bis-diazotized benzidine. The antibodies to TSH showed extensive cross reacitions with other pituitary hormones. The antibodies to ACTH appeared to be hormone specific but not species specific. Antibodies to bovine, porcine, and human growth hormones appeared to be species specific, and for the most part, hormone specific. The application of human growth hormone and ACTH antisera to detection and measurement of these hormones in human body fluids is in progress.