W e examined the status of p53 mutation, a putative tumor suppressor gene, in cultured normal human salivary gland cell clones, which had been immortalized by transfection with origin-defective mutant DNA of SV40. In this study, we employed two anti-p53 antibodies, PAb1801 and PAb240, both of which are murine monoclonal antibodies specifically reactive with p53 products. The characteristics of these antibodies are as follows: PAb1801 detects both wild and mutant forms of human p53, whereas PAb240 is only reactive with humanmutant p53. When expression of p53 was analyzed by both immunocytochemical staining and immunoblot, cell clones were found to express wild-type p53, but not the mutant form of p53. These results, therefore, indicate that normal human salivary gland cell clones transfected with SV40 DNA contain wild-type but not mutant-type p53.