Fewer than 40 years ago heat shock proteins (HSPs) seemed to many researchers little more than a curiosity in Drosophila. Elizabeth Craig, professor of biomolecular chemistry at the University of Wisconsin, Madison, remembers that some scientists used to regard HSPs as "something weird that a fruit fly does." She has been studying these proteins and the genes responsible for them in yeast for more than two decades. Today HSPs are the object of intense work by scientists in the United States and abroad as a potential means of both providing vaccines to treat cancer and other diseases and increasing understanding of the immune system. HSPs as vaccines would be a novel approach to disease treatment. "They can be used as carriers, vectors, and in that regard offer a promising future," says Alberto Macario, a research physician at the New York State Health Department.