For out of olde hokes, in good feyth, Cometh all this newe science that men lere. Geoffrey Chaucer The Parliament of Fowls During the past two decades knowledge of the human menstrual cycle and of normal and abnormal reproduc- tive function has increased at a dramatic rate. As rec- ognized in this volume, this explosion of knowledge is due in large measure to the development of radio- immunoassays for the measurement of the minute quantities of reproductive hormones found in the cir- culation. Yet the foundations for the many recent developments were laid well in advance. The concepts and...