A review has been presented of the biochemistry and pharmacology of a class of natural products, the flavonoids. These substances which are widely distributed in the plant kingdom and present in considerable quantities in common food products, spices and beverages have in a concentrated form (Propolis) been used since ancient times by physicians and laymen to treat a great variety of human diseases but they have yet to pass the tests of modern, controlled, clinical experimentation. An attempt has been made to present the fundamental evidence from the basic biological sciences which is required to stimulate the interest of the clinicians in this new field. The few existing reports on the careful pharmacodynamic, pharmacokinetic and clinical studies which have been made have been summarized to provide a basis for a full-scale investigation of the therapeutic potential of flavonoids.