Genetic testing is becoming big business, but major questions linger about its usefulness. A complete scan starts at about $1,000 and promises clues about a person's ancestry and potential health limitations. The technology has existed for at least a decade, but in recent years the number of options has skyrocketed. However, while correlations of DNA variations and disease susceptibility have grown stronger, the data are incomplete and sometimes conflicting. Only in rare cases can a gene variant reliably predict disease susceptibility. Most conditions are complex, involving myriad biological, behavioral and environmental components. Physicians are unsure how to use the information from pharmacogenomic tests, and it remains to be seen whether knowledge of genetic susceptibility has any power to change people's behavior. A 2006 study by the Government Accountability Office accuses companies of misleading consumers and perhaps not even analyzing DNA. The companies maintain that they are engaged in high-quality, responsible science, offering people information that they can start using now, while genetics research continues to evolve. On another front, Genetic Alliance has begun advocating for regulations to prevent discrimination, safeguard privacy, and ensure quality standards. While such companies as Navigenics, 23andMe and deCODE clearly state that the data remain the property of the customers, they have left the door open to use their databases in the future. For now, the best tool for personalizing medicine the low-tech, low-cost compiling of a family health history.