It is a great honor for me to be invited to give this Soper Lecture. I met Fred Soper only once—at the 6th International Congresses of Tropical Medicine and Malaria at Lisbon in 1958. I had, of course, known of him for a number of years beforehand, and had read with the greatest interest his account of how Anopheles gambiae was halted in its invasion of Brazil and finally expelled from an area of some 18,000 square miles. In his lifetime, Soper was associated with many significant achievements in diverse fields of public health, but to me as a malariologist none compares with his eradication of Anopheles gambiae from Brazil. More than 40 years later, this episode still stands as one of the most significant victories that man has scored over malaria and epitomizes Soper's administrative genius and technological competence.