Abstract
Peroxidase-labeled antibody method was used to localize tissue antigens directly on ultrathin sections. For the demonstration of the method, luteinizing hormone, growth hormone and prolactin were localized on ultrathin sections of methacrylate-embedded anterior pituitary gland of the rat. The hormones were localized in secretion granules and in endoplasmic reticulum, but not in nucleus or mitochondria. This approach totally eliminates the problem of penetration of antisera through tissues and permits better immunologically controlled experiments by using serially sectioned materials.