The lack of molecular markers is a major factor contributing to the poor diagnosis and survival of women suffering from epithelial ovarian cancer. As reported in the January 30 Proceedings of the National Academy of Science, Welsh et al. identified groups of genes whose expression correlated with clinical observations and therefore might be useful diagnostic markers for ovarian cancer (Proc Natl Acad Sci USA 2001, 98:1176-1181). They developed a high-throughput protocol (which they have termed 'arrays-of-arrays') that involved the simultaneous hybridization of samples to 49 individual oligonucleotide arrays on a single glass wafer. They analyzed the expression levels of over 6,000 human genes in normal tissue and 27 malignant ovarian samples in a single assay. The authors report that the arrays-of-arrays technology allows this type of analysis to be performed in less than one week. The hierarchical cluster analysis identified groups of genes that were more highly expressed in either normal or cancerous tissue. The arrays-of-arrays approach enables rapid and systematic identification of diagnostic markers.