The authors have studied the presence and distribution of Insulin-Like-Growth-Factor-1 (IGF-1) in 5 autopsied normal and 20 surgically removed human pituitary adenomas, employing a peroxidase-anti-peroxidase method. IGF-1 could be demonstrated in all cases, with variation of cells immunostaining from 60% in normal pituitary gland to 100% in corticotroph cell adenoma.