High technology and human tragedy; luck and persistence; altruism and competition--they all come together in this absorbing tale of medical detection that spans decades and crosses continents. In 1985, Pollen (Neurology and Physiology/UMass Medical Center) examined an Alzheimer's patient who brought with him a multigenerational family tree representing the most extensive known pedigree of the disease. The records began with ``Hannah,'' an ancestor born in Byelorussia 150 years ago, and included data on dozens of her descendants, living and dead--information, Pollen immediately realized, of great significance to geneticists. Here, he recounts a two-fold tale--that of geneticists determined to find the abnormal gene that causes familial-based Alzheimer's, and of an afflicted family determined to help them. Science basics are provided in a brief look at the work of Gregor Mendel, the founder of genetic science, and of Alois Alzheimer, the 19th-century Bavarian physician who identified the dementia that bears his name. Occasionally, the technicalities of modern molecular genetics may slow the general reader down, but Pollen doesn't lose sight of the human story: In one chapter, he describes his own mother's descent into dementia. The author also explains that, despite the 1991 linking by British researchers of a mutation in a specific gene to one form of familial Alzheimer's, the key to the vast majority of cases remains to be found. Teams of researchers in England, Belgium, Canada, and the US are competing fiercely to be the first with new findings, prompting Pollen to question the roles of competition and cooperation in modern medical research. In spite of some difficult technical passages: an exciting story that reveals much about how science is done--and that says something affirmative about the human spirit as well. (Eleven illustrations--not seen).