A great deal of new information has arisen in the past 2 years concerning the physiology of inhibins and their clinical relevance in reproductive medicine. It is now recognized that the two inhibin isoforms, inhibin A and inhibin B, are produced by the gonads in the course of gamete maturation and have different patterns of secretion during the menstrual cycle. Inhibins are also produced by the placenta and fetal membranes and may be involved in physiological adaptation of pregnancy. Clinically, inhibins may serve as sensitive tumor markers in postmenopausal women, or as useful tools for evaluating ovarian reserve in infertile women; they may also be used in the diagnosis of materno-fetal disorders.