Comparative genomic hybridization (CGH) provides genome-scale overviews of chromosomal copy number changes in tumors (1 ). Unlike conventional cytogenetic analysis, it needs no cell culturing, making it applicable to practically any kind of clinical specimen from which DNA can be obtained, including archival paraffin-embedded material (1 ). CGH maps the origins of amplified and deleted DNA sequences on normal chromosomes, thereby highlighting locations of important genes. However, this technique cannot detect chromosomal translocations, inversions, or subchromosomal changes. By its nature, CGH is especially suitable for screening tumors in various stages of development, such as premalignant lesions and invasive carcinomas and metastases, pointing out the location of possible oncogenes or tumor suppressor genes that may play a role in the early onset of malignancy or in the process of metastasis. In addition, CGH can be used to compare different histologic components within one tumor, enabling a better understanding of the relation between phenotype and genotype, or to compare derivative cell lines with the original cell line.