The modification of the behaviour of certain cancers, particularly of breast and prostate, by alteration of their endocrine environment, has attracted much attention in the past ten years. An understanding of this aspect of the work is necessary if hypophysectomy is to be used intelligently as a therapeutic measure, and as a moans of providing further information about the factors involved in the initiation and promotion of cancer. The situation was reviewed by PYRAH in 1956, and adrenalectomy and hypophysectomy were discussed by ATKINS and others at a meeting of the Royal Society of Medicine in 1957, but a Conference at the University of Glasgow in 1957 considered the matter in its widest aspects, and its proceedings (CURRIE 1957) provide at the moment probably the most comprehensive and detailed review, although a more recent analysis of the endocrine aspects of breast cancer has boon contributed by WELBOURN (1959) and provides the most up-to-date summary of current ideas.