Excerpt from William Blum, "Since I Gave Up Hope, I Feel Better" (enigmatic title):

"Consider this: On June 9, 1969, Dr. Donald M. MacArthur, Deputy Director, Research and Engineering, Department of Defense, testified before Congress:

'Within the next 5 to 10 years, it would probably be possible to make a new infective microorganism which could differ in certain important aspects from any known disease-causing organisms. Most important of these is that it might be refractory [resistant] to the immunological and therapeutic processes upon which we depend to maintain our relative freedom from infectious disease.'[11]

"Whether the United States actually developed such a microorganism and what it did with it has not been reported. AIDS was first identified by the US Centers for Disease Control and Prevention in 1981. It's certainly possible that the disease arose as a result of Defense Department experiments, and then spread as an unintended consequence."

http://www.informationclearinghouse.info/article19855.htm