Google X, the secretive research arm of Google Inc, is making a major foray into clinical research with the goal of pinning down what it means to be healthy. The Mountain View, California, company revealed last week that it will launch a project, the Baseline Study, to follow thousands of people and identify patterns of biochemicals, proteins, genetic mutations, and other measurements that correlate with who remains well and who gets sick.

The project was first reported on 24 July by The Wall Street Journal, whose story described it as Google’s “most ambitious and difficult science project ever” and “a giant leap into the unknown.” It will “know the structure of thousands of people’s bodies—down to the molecules inside their cells,” raising “significant issues of privacy,” according to the article.

After a pilot study this summer with 175 people who are donating blood and saliva for testing, Google X expects to recruit thousands more volunteers in collaboration with medical schools at Stanford University in Palo Alto, California, and Duke University in Durham, North Carolina. Besides donating biological samples, participants may sport wearable medical devices, such as a glucose-sensing contact lens developed by Google X. Heading the project is Andrew Conrad, Google X’s life sciences chief, who developed cheap HIV tests for donated blood and was chief scientific officer of LabCorp, the giant clinical testing firm, before joining Google last year.

The study may also find new correlations with physiological measures and better define what’s normal: For example, perhaps monitoring pulse 24 hours a day might reveal some new predictor of a heart attack, according to collaborator Robert Califf, a Duke cardiologist. Carduiff said the study hopes to recruit 10,000 volunteers over 2 to 3 years from Palo Alto and the cities of Durham and Kannapolis in North Carolina.