In 1992, a small biotech company in Cambridge, England announced the creation of "Astrid," the world's first "transgenic" pig. Soon scientists were talking seriously about "organ farms" that would solve the world's chronic shortage of hearts, livers and other spare parts for human transplantation. A new breed of pigs, genetically-altered to be more human--and,so, less likely to be rejected by the immune systems of human recipients--was riding into town to save the day.

Now, five years after the first clinical human trials were first predicted to have begun, the most hopeful members of the xeno community still see trials several years away, and a number of scientists and scientific organizations are expressing new cautions. At the same time, a new possible solution to the organ shortage--creating organs from human stem cells, then cloning them--has emerged as a potentially more promising long-term solution. All of this is effecting the business of xeno: The science ultimately might prove workable, but will the money for the research hold out through more years of unprofitability and potential controversy?

The current wave of cautions about xeno is in no way the last word, and growing organs from human stem cells is not without serious problems of its own: Stem cell science is in its infancy, and the research quickly runs into two deeply contentious ethical and political debates--abortion and cloning--which could prevent it from progressing, at least in the United States. This brings everyone interested in solving the world's organ shortage back to the original riddle: Will the world's transgenic pigs ever fly? The answer is no joke to the companies who have staked almost a billion dollars over the last decade on making it happen.