A pharmaceutical formulation for oral administration containing root, bark and wood of Philippine Narra tree (Pterocarpus Indicus) in dried powder form in sachet in a unit of 2 to 3 grams and made into a decoction of 8 ounces or in capsule in a unit of 100 to 300 milligrams at a dosage of three to six times a day can enhance the immune system of a person and can be used for the prevention and treatment of INFECTIOUS DISEASES.