There is a prov1s10n in the charter of each Study Section of the Division of Research Grants at the National Institutes of Health that stipulates that "workshops" are to be held periodically to aid Study Section members in their appraisals of recent developments in their fields and to identify future challenges worthy of investigation. The Reproductive Endocrinology Study Section was established on December 13, 1985 to review research grants and research training activities relating to reproductive endocrinology, including aspects of management of reproductive endocrine disorders and hormonal imbalances as related to infertility and during pregnancy and puberty, breast cancer and prostate cancer. It held its first workshop, entitled, "Autocrine and Paracrine Mechanisms in Reproductive Endocrinology," in October, 1988 in Shrewsbury, MA at The Worcester Foundation for Experimental Biology. The proceedings of this workshop, which are detailed herein, reflect the fact that autocrine and paracrine interactions are rapidly being accepted as an exciting area of research by scientists investigating the physiological and biochemical mechanisms of hormone action in the male and female reproductive systems. The material covered is novel and wide-ranging, extending from theoretical considerations of mechanisms of growth factor action and the role of cell cycle stage in determining hormone action to investigations of autocrine and paracrine interactions during development to discussions of the potential clinical ramifications of the basic research findings. Such an extensive inventory is necessary for two reasons.