ProbeMatchDB is a web-based database designed to facilitate the search of EST/cDNA sequences or STS markers that can be used to represent the same gene across different microarray platforms and species. It can be used for finding equivalent EST clones in the Research Genetics sequence verified clone set based on results from Affymetirx GeneChips. It will also help to identify probes representing orthologous genes across human, mouse and rat on different microarray platforms.