Davies (editor of the journal Nature Genetics) and White (coauthor, Einstein: A Life in Science, 1994) describe one of the most dramatic discoveries to date regarding the influence of genetic factors on health--the most exciting frontier in medical research. The authors relate the discovery and its background in full detail, providing an effective foundation for understanding not only the process of locating the breast cancer gene but, more generally, the nature and treatment of breast cancer. Cancer is the result of an error in the DNA that regulates normal cell division, caused either by an external agency, such as radiation, or by a congenital ""mistake"" in the DNA. The fact that having close female relatives with breast cancer greatly increaseed a woman's odds of getting the disease indicated that a faulty gene might be active in these cases. By the late 1980s, research zeroed in on a gene designated BRAC1, the chromosomal location of which was announced in 1990 by Dr. Mary Claire-King of the School of Public Health at Berkeley. King's discovery--which the authors compare to narrowing down a search for a missing person from all of North America to New York--set off a race among researchers to pinpoint the precise location of BRAC1. King joined forces with Francis Collins, whose laboratory had isolated the genes responsible for cystic fibrosis and Huntington's disease. But in October 1994, a team headed by Mark Skolnick of the University of Utah isolated the gene. While the discovery does not provide a cure for cancer--or even a clue to one--it may allow women to more accurately assess their own risk. Perhaps in the long run, the discovery will lead to genetic therapy for those women who carry the gene. A well-written and exceptionally detailed overview of the search for the breast cancer gene, spotlighting the breakthrough in its full dramatic impact.