The Chinese hamster tumor-derived cell line 835T2 exhibits specific karyotypic changes, including the loss and/or translocation of genetic material. To investigate whether the p53 tumor suppressor gene was involved in the exchanges, cDNA from primary Chinese hamster cells was isolated by using sense and antisense primers of the human p53 gene. The cDNA was sequenced, and the sequence was compared with the Syrian and human p53 cDNA reported sequences. The sequence homology was very elevated, demonstrating that the cloned fragment contained part of the Chinese hamster p53 gene. The corresponding genomic fragment was also cloned and used as a biotin-labeled probe for in situ hybridization on Chinese hamster chromosome spreads. Hybridization was visualized by avidin-FITC, and the assignment was done comparing the banding obtained with BamHI restriction enzyme and the location of the fluorescent signals pattern of the same metaphase. The signals revealed that the p53 gene (TP53) is localized on Chinese hamster chromosome band 2p31, which is not involved in the karyotypic changes specific to the 835T2 cell line.