Expert researchers who have developed and applied significant new assays describe in step-by-step detail a variety of methods for measuring a broad variety of hormones, related peptides, and synthetic steroids in various biological fluids. The hormones measured range from glucocorticoids in biological fluids, urinary steroids, aldosterone in blood, and plasma renin activity, to gut hormones in plasma, melatonin, prolactin, 6-sulfatoxymelatonin, and androgens in blood, saliva, and hair. The emphasis is on noncommercial assays so that investigators can set up novel methods suited to their special needs. Commercial assays are also described for comparative purposes. Tutorials on radioimmunoassay, gas chromatography-mass spectrometry, high-performance liquid chromatography, and PCR techniques help the reader to choose the best method for his or her purpose.