Adapted from the authors' Pulitzer Prizewinning series for the Chicago Tribune, a detailed look at the cutting edge of medical research: attacking disease by repairing inherited flaws in the cells of the human body. Gene therapy is potentially as revolutionary as Pasteur's germ theory of disease, especially as science uncovers more and more diseases that can be traced to genetic defects. It is also fraught with controversy, as many researchers urge extreme caution in the introduction of foreign genetic material (often derived from viruses) into the human body. Others (notably William French Anderson, formerly director of the molecular hematology department of the National Institutes of Health) want to push forward with therapies that promise to eradicate genetically based diseases. It is easy to understand this attitude when reading about Lesch-Nyhan syndrome, in which patients have to be restrained to prevent them from attacking their own bodies (as well as those tending them) with their teeth, or adenosine deaminase deficiency, in which the body has no defenses against infection. The authors put often epic political battles in the context of the personal quests of the scientists (who foresee Nobel prizes for the successful pioneers) and of the poignant case histories of the first patients to come forward as guinea pigs for the new therapies (some of whom are now living comparatively normal lives). The second half of the book looks at prospects for future developments in gene therapy, from the prevention of heart disease to the tailoring of drugs to attack tumors in specific locations. Lyon and Gorner also glance at the disturbing potential of genetically enhanced intelligence, and other ``cures'' suggestive of a revived science of eugenics, with all its ethical complexities. Well written, exhaustively researched, and filled with the human stories of the scientists, the doctors, and the patients whose only hope is this new field of medicine.