Abstract
Various recent researches have provided the scientific basis to the observations of ancient scholars regarding the rhythmic variations in human physiology and disease in relation to temporal and environmental factors. The field of chronobiology is rapidly expanding around the world and became the major concern of research in every aspect of human biology like in the study of genetics, endocrinology, pharmacology, medicine, ecology etc. Although the chronobiology has been considered as new branch of human biology but its roots are in ancient archives and cultural practices. Ancient Ayurvedic scholars have very well observed and documented the temporal and environmental influences on rhythmic variations (diurnal and seasonal) in functional state of Tridosha (biological entities derived from Panchamahabhuta, responsible for regulation of all bodily functions and regulations, Agni( bio fire) responsible for digestion and metabolism), Sharir Bala (immunity) and disease propensity with respect to age, day and night, and season as well as the physiological adaptation to it. Ayurveda has described Dincharya (daily regimen) Ritucharya (seasonal regimen) to balance the Doshika fluctuations/circadian rhythm in metabolism as relates to time factor and to maintain homeostasis with environment. The aim of this article is to bring attention about the observations and descriptions contained in Ayurveda. The scholars and researchers of Modern / Cosmopolitan Medicine will be elucidated worldwide in general and scientists working in the field of chronobiology, chronopharmacology and preventive medicine in particular. The percolation of wise Ayurveda concepts, in present health care policies will help in de-westernisation of ailing Indian Health Care delivery. It will make clinical practice of preventive medicine, relevant and easier than ever.

Key words: Kala, Ritu, Chronobiology, Dincharya, Ritucharya, Dosha, Agni, Prakriti