Amplification of MDMZ and CDK4 is observed frequently in human sarcomas. Although overexpression of these protooncogenes might inhibit growth regulation through the TP53-and retinoblastoma tumor suppressor protein (RB)-mediated pathways, neither gene was included consistently in all of the amplicons observed in our sarcoma panel. It was unclear whether both of these genes were selected for during amplification. Furthermore, in some samples without amplification of MDMZ or CDK4, comparative genomic hybridization showed amplification in the 12q I 3-1 5 region, suggesting that another selection mechanism might also be involved. To investigate the possibility that another target gene, which may be located between CDK4 and MDM2, could be the driving force, we characterized the involvement of 17 loci from this region in 12ql3-15 amplicons that were detected previously in 21 sarcoma samples. The results showed discrete amplicons around MDMZ and CDK4 with reduced amplification of the intervening sequences. This suggests that there is separate selection for amplification of the two genes, and it makes the possibility of a common selective gene unlikely. Furthermore, DI 2S8, localized distal to MDM2, was amplified almost as frequently as MDMZ and was also amplified in one of the samples without MDMZ or CDK4 amplification. The data suggest that amplification of at least three different regions within the 12q I 3-1 5 segment may be selected for in tumor cells involving MDM2, CDK4, or a more distally located gene, possibly near D I2S8. Genes Chrornosorn Cancer /7: 254-259 (1996).