Immunopharmacology is defined as that part of pharmacology that deals with drugs acting on the immune system and, in addition, with the pharmacological actions of substances derived from the immune system. In order to lend sharper definition to the term immunopharmacology the subject matter has been divided according to clinical and pragmatic criteria. The division into immunosubstituion, immunosuppression, antiallergic substances and immunostimulation gives the heterogeneous material a tighter structure than would any classification according to origin, chemical structure or mechanism of action.