Reproduction is, it would appear, a very simple biological event: the result of an act of love. In actual fact, it has always been, and still continues to be, one of the most complex, yet at the same time, most fascinating, problems, with which Science has ever been engaged. Physiopathology of human reproduction has always made use of investigations of a morphological nature, perhaps on account of the need to "see inside" the reproductive apparatus or within the gonads themselves in order to better understand how they function. Observation of spermatozoa practically coincided with the discovery of the microscope, and histological study of the testis and ovary was, for a very long time, the only means available with which to closely follow the evolution of gametes destined to their meeting. Improvement of techniques resulting from the evolution of endocrinology of reproduction has only apparently put aside morphological techniques, whilst at the same time there has been a gradual development of ultrastructural techniques, on the one hand, and, on the other, macroscopic diagnostic systems through images.

Impending famine and a terrifying rate of consumption of natural resources are vital issues which have focussed public interest in the ecologic, social and political problems of ever increasing overpopulation in many countries of the world. As well as the vast material and intellectual expenditure lavished on family planning and birth control, the past decade has seen an immense research effort in the elaboration of improved methods of fertility control, both for men and for women. During the same period, however, research into the causes of male fertility disorders has proceeded with equal intensity, and a number of promising therapeutic approaches have become the subject of clinical trials. The wish of an individual or of a couple to have offspring is an absolute which requires no further justification, and there can be few challenges to a physician as essential as the spouses' predicament in a childless marriage. Only with a special knowledge of the function, pathology and pathophysiology of the reproductive system is he properly equipped to meet that challenge.

This monograph brings together our work concerning the relationships be tween the hypothalamus, pituitary and testis. The studies span approximate ly a decade of collaborative work. Over this period our contributions and those of many others have advanced greatly our understanding of many aspects of male reproductive biology. This monograph attempts to survey these developments and to highlight many unresolved issues. It also provides an opportunity to demonstrate the value of investigations which relate bio chemical to structural parameters and to illustrate the importance of animal studies in elucidating biological principles with clinical applications. The reverse is also important since the pathophysiology of human disorders of ten provides insight into hitherto unsuspected basic mechanisms. In any rapidly expanding field it is difficult to stop revising and extending a manuscript. It is equally difficult to quote every reference in the field but we trust that those of significance have not been omitted. Some of our former students have collaborated with us as co-authors in producing this monograph. It is equally important to recognise the contributions of our other former students and colleagues who have physically participated in the studies and without whose intellectual contributions a number of concepts would not have been elucidated. Their work is acknowledged in the text of the monograph and the extensive list of references."