"In order to get the answers you want, you need to do all the concentrations, all the times, and that's why you need to have a high-throughput system," Austin says.

Researchers at the NIH have already used high-throughput screening to test several thousand chemicals over a range of 15 concentrations varying by several orders of magnitude, and for exposure times ranging from minutes to days. The chemicals they picked have well-known toxic effects, gleaned from animal studies. By comparing data from high-throughput tests with that from animals, researchers should be able to fine-tune cell-based tests so that they're at least as reliable and as informative as animal experiments.

"Animals are not always giving us the right answer," says John Bucher, associate director of the National Toxicology Program, "so we need to use all the information we can get from different systems."

In a sense, Austin says, this new approach turns the animal-testing procedure "upside down." Rather than giving a rat a chemical and then dissecting the animal and examining its tissues to see the effect of the compound, metaphorically, "we are dissecting the rat first into its component cells, then computationally putting the rat back together."

However, it will take years for researchers to prove--if they can--that cell-based toxicity screening can supercede animal tests so "you cannot abandon animal testing overnight," Zerhouni says. "It will have to be intertwined for a few years."