Section headings and selected papers. Preface (L. Wetterberg). Special Lecture. Biological rhythms: from gene expression to behavior (J.S. Takahashi). Light and Light Perception. Light - definitions and measurements (R. Wibom). The mammalian melatonin rhythm generating system (D.C. Klein). Maternal entrainment of a fetal biological clock (S.M. Reppert, D.R. Weaver). Anatomy and Physiology of Light Regulated Endogenous Oscillators. Daily melatonin infusion entrains free-running activity in Syrian and Siberian hamsters (R. Kirsch et al.). The use of melatonin as a marker for circadian phase and as a chronobiotic in blind and sighted humans (A.J. Lewy, R.L. Sack). Light Influence on Circadian Rhythms. Overview: unmasking temperature data obtained in field conditions (J. Waterhouse et al.). Some effects of light and melatonin on human rhythms (J. Arendt). Circadian, Menstrual and Seasonal Light Regulated Rhythms. The influence of age, sex, height, weight, urine volume and latitude on melatonin concentrations in urine from normal subjects: a multinational study (L. Wetterberg et al.). Circadian variation of some endocrine and neuroendocrine functions in humans (Y. Touitou, E. Haus). Light Treatment of Disorders with Rhythmic Disturbances. A comparison of two different placebo-controlled SAD light treatment studies (C.I. Eastman et al.). Diagnostic Implications of Seasonality and seasonal affective disorders: diagnostic implications for the outcome of phototherapy (J. Beck-Friis). Afterword. Index.