The specific time that patients take their medication is very important as it has significant impact on treatment success. The pharmacokinetics and pharmacodynamics of an Ayurvedic medication is directly affected by biological activities of the body. The effectiveness of many drugs depends on the dosage administration time. In Ayurveda it has been told that rhythmic changes in the predominance of bodily Doshas occur. (Ashtang Hridaya Sutrasthana 1/7-8). Bheshaja Sevana Kala based on this concept of Doshas. Aacharyas have mentioned Bheshaja Sevana Kala in varying numbers. An attempt to correlate these Kala has been made. In the modern science this concept of timed dosage is known as chronotherapeutics. It was seen that all the Kalas can be incorporated in only five Kalas told by Sharangdhara.