Objective To determine whether the previously isolated transforming sequence, designated the Tx gene, which was derived from a Chinese human nasopharyngeal carcinoma (NPC) cell line CNE-2, is mutated in NPC cell lines and biopsy tissues.Methods DNA samples prepared from various cell lines and 11 cases of NPC biopsies were subjected to analysis with the modified polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) silver staining technique to screen for possible point mutation(s).Results Mobility shifted bands were revealed in two NPC cell lines, CNE-2 and HONE-1, but not in non-NPC cell lines, including stomach cancer cell line HGC-1, colon cancer cell line SW-480 and cervical cancer cell line HeLa. No sequence changes or polymorphisms were found in 11 cases of primary NPC biopsies.Conclusions In most cases of NPC, activation of this transformation-associated sequence does not involve a mechanism of gene mutation. The role played by this gene in NPC is to be further determined.