AbstractDNA extracts from hepatocellular carcinomas of 13 patients from South Africa were examined for hepatitis B virus (HBV) DNA sequences by molecular hybridization using [32P]‐labeled recombinant, cloned, and purified HBV‐DNA. Eight patients were HBV carriers as demonstrated by the presence of hepatitis B surface antigen (HBsAg) in their serum, and each of these patients had HBV‐DNA sequences in hepatocellular carcinoma tissue. Five patients who were not HBsAg carriers, did not have HBV‐DNA in their tumors. In DNA extracts from all tumors of patients who were HBsAg‐positive, the HBV‐DNA was integrated into the host genome. The integration pattern was unique for each tumor, but HBV‐DNA bands of a given length were present in more than one specimen and in a human hepatocellular carcinoma cell line (PLC/PRF/5). These results suggest that integration of HBV‐DNA into the human genome occurs in conjunction with malignant