In the past ten years, as more refined techniques for evaluation of hormone secretion have evolved, a number of patients suffering from a deficiency of a single anterior pituitary hormone have been described. Although symptoms and physical findings of patients suffering from panhypopituitarism are contained in most textbooks of endocrinology, this is often not true for patients with isolated deficiencies of pituitary hormones. The purpose of this paper is to present and clarify some aspects of the symptomatology, physical findings, and diagnosis of isolated pituitary hormone defects. Isolated deficiencies of adrenocorticotropin, thyrotropin, somatotropin, and gonadotropins have been described. Each of these will be discussed and exemplary case histories presented. The Isolated Deficiency of Adrenocorticotropic Hormone (ACTH) At least ten patients with hypoadrenotropism or the isolated deficiency of ACTH have been described in the literature. The first was probably that of Steinberg et al1 who reported a deeply pigmented woman