The use of biological agents, also known as biological weapons in modern terms, to eliminate enemies and rivals, has been a critical issue in recent decades. The history of political developments in Iran during the Islamic Middle Ages has been witness to many instances of using weaponized biological agents for accomplishing political-military goals. This research employs a historical approach and attempts to identify the functions of biological agents in the political and military developments of Iran during the Islamic Middle Ages. The results indicate that in addition to functioning as an instance of deterring propaganda, thus breaking the enemy's morale, biological weapons were able to alter the balance of military power in the battleground and determine the triumphs and defeats. Accordingly, biological agents have had other military and political implications, such as sabotaging enemies' weaponry and equipment and eliminating prominent figures. Iran's history has documented innumerable instances of such applications of biological weapons during the Middle Ages.
