Knowledge about the history and development of therapeutic agents holds a central position in the education and training of pharmacists and pharmacologists. Students enjoy learning about the discovery of drugs, including details about the pioneer workers involved (apothecaries, organic chemists, pharmacologists, and physiologists) and the role played by serendipity. The treatment of people suffering from allergies and the development of drugs that block the actions of histamine at H-1 and H-2 receptors are the subject of this review. Pharmaceutical products that block H-1 receptors are widely used as prophylactic treatment for seasonal allergies that plague millions of people worldwide. The development of H-2 receptor antagonists revolutionized treatment of gastric hyperacidity, the principal cause of peptic ulcers. Antihistamine research has changed focus toward the development of drugs that block the action of histamine at H-3 and H-4 receptors and the therapeutic potential is gradually being appreciated.