A novel experimental nude mouse model, which is useful for investigation of the mechanisms of PIVKA II synthesis, was established by inoculation with PIVKA II-producing human hepatoma cells (huH-1). We have found markedly elevated levels of PIVKA II in the plasma of nude mice transplanted with huH-1 cells and increased PIVKA II content in huH-1 tumor tissues. Whereas we have not found detectable level of PIVKA II neither in the plasma nor in tumor tissues of nude mice transplanted different human hepatoma cells (HLF) which is not producing PIVKA II. Histology of the tumor tissues produced by huH-1 cells revealed a thick trabecular pattern with blood spaces.