This book is a compilation of edited papers which were presented at the XIth World Congress of Fertility and Sterility held in June 1983 in Dublin, Ireland. Although it has long been known that male factors are responsible in at least 30% of infertile couples only recently have concerted efforts been made on the part of urologists, gynaecologists and basic scientists to identify these factors more precisely. The nature of spermatogenesis is complex but application of various scientific methods have at last opened up new and promising approaches to our understanding of this subject. Clinical results however have been depressing; the majority of treatments lack realistic evaluation and are initiated in hope rather than with a sound scientific basis. We anticipate that this volume will in some small way correct these deficiencies. The papers have been grouped into related topics. The first section deals with the evaluation of the spermatozoa and includes a critical assessment of the recently introduced zona-free hamster egg test of sperm function. Further sections include the biochemistry of gonadal function and the immunology of male reproduction; most papers are concerned with studies in the human. The clinical sections cover medical and surgical approaches to treatment and the final section deals with various aspects of AID practice.