The problem of defining more clearly the status of various steroid-producing tissues and evaluating the metabolic processes involved has challenged biochemists and endocrinologists for many years. This chapter defines a group of C19 steroids as "androgens" and considers their overall metabolism. The naturally occurring androgens share, with modifications, the molecular structure of the C19 steroid compound androstane. Human plasma contains a number of proteins, some of which bind certain hormones specifically. The best known of these are probably the globulins which bind cortisol and thyroxine. The techniques of steroid assay were relatively insensitive and the estimation of plasma androgen levels, particularly in female subjects, posed almost insuperable problems. The excretion of testosterone glucuronide has no direct relationship to the level of circulating testosterone and urinary testosterone glucuronide is not a simple parameter of testosterone secretion. Using radiolabeled steroids, it is possible to study the complex quantitative relationships between the various plasma precursors and the urinary metabolites in normal women.