At first glance, Michael Shuler's chip could pass for any small silicon slab pried out of a computer or cell phone. Which makes it seem all the more out of place on a bench top in the Cornell University researcher's lab, surrounded by petri dishes, beakers, and other bio-clutter and mounted in a plastic tray like a dissected mouse. The chip appears to be on some sort of life support, with pinkish fluid pumping into it through tubes. Shuler methodically points out the components of the chip with a pencil: here's the liver, the lungs are over here, this is fat. He then injects an experimental drug into the imitation blood coursing through these "organs" and "tissues"-actually tiny mazes of twisting pipes and chambers lined with living cells. The compound will react with other chemicals, accumulate in some of the organs, and pass quickly through others. After several hours, Shuler and his team will be closer to answering a key question: is the compound, when given to an actual human, likely to do more harm than good?

This so-called animal on a chip was designed to help overcome an enormous obstacle to discovering new drugs: there is currently no quick, reliable way to predict if an experimental compound will have toxic side effects-if it will make people sick instead of making them well. Testing in animals is the best drugmakers can do, but it is slow, expensive, often inaccurate, and objectionable to many. To minimize the number of animal tests, drug companies routinely screen drug candidates using cell cultures-essentially clumps of living human or animal cells growing in petri dishes or test tubes. The approach is relatively cheap and easy, but it gives only a hazy prediction of what will happen to a compound on the circuitous trip through the tissues and organs of an animal.