New drugs are screened for adverse reactions using a laborious, costly process and still some promising therapeutics are withdrawn from the marketplace because of unforeseen human toxicity. Novel higher throughput methods in toxicology need to be developed. These new approaches should provide more insight into potential human toxicity than current methods. Toxicogenomics, the examination of changes in gene expression following exposure to a toxicant, offers the potential to identify a human toxicant earlier in drug development and to detect human-specific toxicants that cause no adverse reaction in rats.