The recognition of toxicological potential in new chemical entities early on in development would be highly desirable in streamlining and reducing the cost of drug development. Analysis of gene expression profiles using microarrays is one of the most fashionable methods for achieving this objective. The procedure relies on developing a gene expression profile related to compound exposure and then matching this against a database of profiles associated with known mechanisms of toxicity. Studies profiling tumors and associating these with pathology and phenotype have shown the potential of the technique. However, application of the technique in toxicology is only at the preliminary stage. This article examines current state of development in toxicology and its future potential. © 2003 Prous Science. All rights reserved.