A particular point mutation of the tumor suppressor gene p53, namely a G→T transversion at the third base of codon 249, is frequently detected in primary hepatocellular carcinomas from patients living in areas where the levels of dietary exposure to aflatoxin B1 and the rates of infection with the hepatitis B virus are very high. Very recently, a nontumorigenic liver epithelial cell line (HACL-1) with a finite life-span and expressing a number of hepatocyte-specific markers was established from a human hepatocellular adenoma in our laboratory. To analyze the role of mutated p53 in the immortalization of human liver cells, we transfected HACL-1 cells with an expression vector containing a human p53 complementary DNA mutated at the third base of codon 249 and analyzed the consequences of this gene transfer on the growth properties of this cell line. HACL-1 cells transfected with mutant p53 showed no increase in their life-span (when compared with HACL-1 cells transfected with the antibiotic resistance gene alone) and did not grow in soft agar, whereas transfection of wild-type p53 into HACL-1 cells led to a proliferation stop. Thus, these results strongly support the view that the mutation at codon 249 of the p53 gene may serve as a fingerprint for aflatoxin B1-induced hepatocellular carcinomas, but is not, by itself, sufficient to immortalize human liver cells.