The article comments on an article about comparative transcriptomics, a method of using Arabidopsis Affymetrix array to analyze the transcript profiles of two related Thlaspi species with contrasting metal accumulation and tolerance phenotypes. It is said that the need for comparative transcriptomics is often influenced by the presence of traits and properties in one species that are not found in any of the current model species. The use of comparative transcriptomics can be of great significance to discover gene expression profiles in plant species in cases where species-specific complementary DNA is absent.