Somatic mutation of the p53 oncogene/anti-oncogene allele has been shown to be involved in many different human solid tumors. Recently, there have been reports that p53 mutations are found to occur at high frequency (50%) in aflatoxin-related human primary hepatocellular carcinomas (HCC) (Hsu et al., 1991 Nature, vol 350, p. 427; Bressac et al., 1991 Nature, vol 350, p. 429). Most strikingly, a hotspot G to T mutation at amino acid position 249 was identified. These reports appear to contradict our earlier publications that although p53 mutation is found frequently in human HCC cell lines, it is rarely found in primary tumors. In this paper, we have further examined 20 different primary HCC samples (17 were hepatitis B surface antigen positive) and their adjacent nontumourous tissues, using restriction fragment length polymorphism (RFLP) analyses. Clear loss of heterozygosity (LOH) was found in only 3 out of 20 samples. All three samples were also found to carry a point mutation within the remaining p53 allele. None of these mutations was found to be at the proposed aflatoxin hotspot of amino acid 249. All three point mutations are of somatic origin. Ten samples, randomly chosen from the remaining 17 LOH negative HCC tumors, were analyzed further by DNA sequencing and Western blot analyses. No point mutations of p53 were found. Taken together with our previous report (Hosono et al., 1991, Oncogene vol 6, p. 237-243), we conclude that p53 mutation occurs infrequently, only approximately 18%, in HBV-positive primary hepatomas from Taiwan. Furthermore, p53 mutation appears to be acquired later in tumor development at least in some HCC samples.