Alexander Fleming's discovery of penicillin while examining a stray mold in his London laboratory in 1928, and its eventual development by a team at Oxford University headed by Howard Florey and Ernst Chain, led to the introduction of antibiotics: the most important family of drugs of the modern era. Before World War II ended, penicillin had saved the lives of hundreds of thousands of soldiers. Almost immediately it also defeated major bacterial scourges, such as blood poisoning and pneumonia, scarlet fever and diphtheria, gonorrhea and syphilis - and, not incidentally, helped to foster a sexual revolution as well as a medical one.<BR>The story of how the mold's active ingredients were isolated and transformed into the world's first wonder drug is little known. Likewise the credit for penicillin development is largely misplaced; Eric Lax explains why almost everyone remembers Fleming and almost no one remembers Florey and Chain. The development of penicillin was the last of four advances in a period of 150 years to deal effectively with infection. Unlike the other three discoveries, whose lifesaving qualities were immediately evident, the efficacy of the penicillin mold could not be determined until Florey's team performed its own laboratory magic.<BR>Neither Fleming nor Florey ever made a dime from their achievements (though Fleming, Florey, and Chain did share a Nobel Prize). Nor did the British pharmaceutical companies grasp the potential of this new drug when it was first presented to them; instead it was the American labs - Merck, Abbot, Pfizer - who won patents on penicillin's manufacture and drew enormous royalties from its sale. Why it took twelve years to develop penicillin, and how it was finally accomplished, is a story of quirky individuals, brilliant science, shoestring research, wartime adventures, the birth of big-time drug companies, and the dramatic passage of medicine from one era to the next.