Recently, two studies have shown that the use ofgene-expression profiling using DNA microarrays or DNA chips may improve the classification of acute myeloid leukaemia (AML). In both studies, cluster analyses based on the molecular signatures defined known subgroups as well as novel subgroups of AML. Chromosomal lesions, mutations, and abnormal gene expression with prognostic value determined the clustering. In fact, gene-expression profiling recognized leukaemias with certain chromosomal aberrations that had been missed by routine cytogenetics. Thus, gene-expression profiling allows a comprehensive classification of AML that includes previously-identified genetically-defined as well as novel prognostically-relevant subgroups. One comprehensive DNA chip may in the future replace a variety of cytogenetic, immunological and molecular techniques that are currently used in combination.