Dear Paolo, Cross validation in what context? If you are looking for cross validation for microarray studies, a quick search on Current Index to Statistics www.statindex.org) turned up only one article: Raghavan, Nandini, Amaratunga, Dhammika, Nie, Alex Y. and McMillian, Michael (2005) Class prediction in toxicogenomics Journal of Biopharmaceutical Statistics, 15, 327-341 Keywords: Classification; Cross validation; GENE EXPRESSION; gene selection; Hepatotoxicity; linear discriminant analysis; Microarray; Normalization; Toxicogenomics Maybe a search on PubMed (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed) for cross validation + your subject of interest would result in more articles. Good Luck, Monnie Monnie McGee, Ph.D. Assistant Professor Department of Statistical Science Southern Methodist University Ph: 214-768-2462 Fax: 214-768-4035