Biological rhythmicity has been a subject of scientific research for a relatively short time. In the special case of daily, or circadian rhythms, it is only during the past twenty years that rapidly increasing efforts have been undertaken in evaluat ing properties and mechanisms. As a consequence of these efforts, the study of biological and, in particular, circadian rhythmicity is no longer a somewhat dubious occupation but rather a serious branch of science which combines the interdisciplinary efforts of numerous researchers around the world. The general result of these efforts is that many features of circadian rhythms of many different species of living beings are well known today. In addition to studies with lower organisms, the evaluation of human circadian rhythms was originally more or less a compulsory exercise done in order to extend the "catalogue of species"; of course, the work was of unusual impor tance due to the special position of man in biology. In the course of the very first experimental series, it became clear that humans possess an "internal clock" as had been established in various organisms, protists, plants, and animals, and that human circadian rhythms fit the general regularities of biological rhythms known at that time. However, it soon became apparent that circadian rhythmicity of man shows, additionally, particularities of great general interest, for practical and theoretical reasons.

Circadian Rhythms and the Human covers the basic principles behind the human circadian rhythms. This book is composed of 12 chapters that discuss the detection, analysis, and definition of rhythms, specifically exogenous and endogenous rhythms. This book also demonstrates the mechanism of metabolic and gastrointestinal rhythms. The opening chapters deal with the rhythms in living organism; establishing the endogeneity of rhythms; definition of nychthemeral rhythm; methods of measuring the frequency of rhythms; exogenous effects upon the temperature rhythm; interaction between exogenous and endogenous influences; and possible origins of renal rhythmicity. The succeeding chapters consider the effect of exercise at different times of day and the concept of sleep-wakefulness rhythm. The discussion then shifts to the effects of repeated time-zone transitions and the effects of time on drug administration. The closing chapters are devoted to the assessment of work performance during shift work. The book can provide useful information to doctors, students, researchers, and the general reader.

Interest in biological rhythms has been traced back more than 2,500]ears to Archilochus, the Greek poet, who in one of his fragments suggests ",,(i,,(VWO'KE o'olos pv{}J.tos txv{}pW7rOVS ~XH" (recognize what rhythm governs man) (Aschoff, 1974). Reference can also be made to the French student of medicine J. J. Virey who, in his thesis of 1814, used for the first time the expression "horloge vivante" (living clock) to describe daily rhythms and to D. C. W. Hufeland (1779) who called the 24-hour period the unit of our natural chronology. However, it was not until the 1930s that real progress was made in the analysis of biological rhythms; and Erwin Bunning was encouraged to publish the first, and still not outdated, monograph in the field in 1958. Two years later, in the middle of exciting discoveries, we took a breather at the Cold Spring Harbor Symposium on Biological Clocks. Its survey on rules considered valid at that time, and Pittendrigh's anticipating view on the temporal organization of living systems, made it a milestone on our way from a more formalistic description of biological rhythms to the understanding of their structural and physiological basis.

With the invitation to edit this volume, I wanted to take the opportunity to assemble reviews on different aspects of circadian clocks and rhythms. Although most c- tributions in this volume focus on mammalian circadian clocks, the historical int- duction and comparative clocks section illustrate the importance of various other organisms in deciphering the mechanisms and principles of circadian biology. Circadian rhythms have been studied for centuries, but only recently, a mole- lar understanding of this process has emerged. This has taken research on circadian clocks from mystic phenomenology to a mechanistic level; chains of molecular events can describe phenomena with remarkable accuracy. Nevertheless, current models of the functioning of circadian clocks are still rudimentary. This is not due to the faultiness of discovered mechanisms, but due to the lack of undiscovered processes involved in contributing to circadian rhythmicity. We know for example, that the general circadian mechanism is not regulated equally in all tissues of m- mals. Hence, a lot still needs to be discovered to get a full understanding of cir- dian rhythms at the systems level. In this respect, technology has advanced at high speed in the last years and provided us with data illustrating the sheer complexity of regulation of physiological processes in organisms. To handle this information, computer aided integration of the results is of utmost importance in order to d- cover novel concepts that ultimately need to be tested experimentally.

Prestigious contributors describe the genetic, molecular, anatomical and neurochemical mechanisms and pathways that operate to regulate and control circadian rhythmicity and functioning in organisms ranging from unicellular algae to human beings. Also considers the implications of the basic and clinical research for humans.