These Proceedinqs of the Midwest Conference on Endocrinology and Metabolism are being published by Plenum Press for the first time. Earlier Proceedings in the series Vlere published by the University of Missouri at Columbia. The shift to an internationally recognized pub­ lisher reflects the considerable growth in stature that the Midwest Con­ ferences have undergone since their inception nine years ago. Originally concerned only with the endocrinology of the thyroid, the Conferences now explore other endocrine areas. Efforts are made to assemble a panel of speakers selected from different sub-disciplines within endocrinology for the purpose of addressing a common problem. The Ninth Conference typifi es til i s approach. The format used in recent Conferences is not unique, but is unfor­ tunately encountered too rarely. A few prominent scholars are invited to come together to expound their findings and concepts in considerable depth, and to participate in a discussion which, together with the for­ mal presentation, is published in the Proceedings. The discussion, noted for its unhurried nature, permits wide participation by the audi­ ence. The subject of the Ninth Conference is one which is basic and im­ portant not only to endocrinology but also to biology in general. Many, possibly most, life processes change in a rhythmic fashion, with similar states recurring at regular time intervals. This rhythmic property of living systems expresses itself as a recognizable and definable pattern or "time-form" in a manner equivalent to the more customary spatial­ form.