Many gene products associated with the cyclin-dependant kinases (CDKs) have been shown to regulate the active kinase complex during the transition points of the cell cycle. Some of these proteins have been implicated in human neoplasia, acting as either oncoproteins or tumour suppressors. The CDK2/cyclin A kinase complex can complex with several proteins, including p21 and PCNA or p45 p19, and p9. It was previously shown that at least two of these proteins, p19 and p45, are abnormally regulated in transformed cell lines. We describe here the mapping by fluorescence in situ hybridization of the gene for the CDK2/cyclin Aassociated protein p45 (SKP2) to 5p13 and the p19-related genes p19A (SKP1A) and pl9B (SKPIB) to 7q11.2 and 12p12, respectively. All three of these loci are associated with karyotypic alterations, known amplifications, or suspected tumor suppressor genes.