As a college sophomore, Elizabeth Holmes envisioned a way to reinvent old-fashioned phlebotomy and, in the process, usher in an era of comprehensive superfast diagnosis and preventive medicine.

That was a decade ago. Holmes, now 30, dropped out of Stanford and founded a company called Theranos with her tuition money. Last fall it finally introduced its radical blood-testing service in a Walgreens pharmacy near company head­quarters in Palo Alto, California. (The plan is to roll out testing centers nation­wide.) Instead of vials of blood—one for every test needed—Theranos requires only a pinprick and a drop of blood. With that they can perform hundreds of tests, from standard cholesterol checks to sophisticated genetic analyses. The results are faster, more accurate, and far cheaper than conventional methods.