A brief history is presented of the isolation and characterisation of the principal steroid hormones affecting reproductive processes with particular reference to progesterone. Section I is concerned with information on the presence and concentration of progesterone and related ketosteroida in human fluids and tissues' and contains a review of the development of chemical methods for the extraction, purification' separation and determination of these compounds. A description is given of spectrophotometrie and gas liquid radiochromatographic methods developed during the present study. The results from the application of these methods to human subjects during pregnancy and the menstrual cycle are presented and discussed. In section II an investigation is reported, into the capacity of blood to metabolise the hormone. This aspect is followed by in , vitro studies upon the biosynthesis heats and role of progesterone as an intermediary compound in the formation of androgens and oestrogens in the human ovary. The results are related to ovarian morphology and a comparison is made between the production and metabolism of progesterone in developing follicles, corpora lutea end postmenopausal tissue. Examples of abnormal ovarian tissue are studied in the same manner and the results compared with healthy tissue. A preliminary investigation into the peripheral metabolism of progesterone in human myometrium is reported as an introduction to studies on transformations which may be related to the mechanism of action, or degradation of the hormone in a target tissue,. Finally some related aspects at progesterone metabolism are presented in a brief review. These studies were undertaken in an attempt to contribute information essential for rational therapy in various form of placental and ovarian dysfunction.