The peripheral benzodiazepine receptor (PBR), is an 18 kDa protein of the mammalian mitochondrial membrane and is a highly conserved protein among the mammalian. PBR is involved in numerous biological functions, including steroid biosynthesis, mitochondrial oxidative phosporylation and cell proliferation. The presence of PBR at the nuclear subcellular level has been demonstrated in aggressive breast cancer cell line and human glioma cells, where it seems to be involved in cell proliferation. In our previous studies we investigated the presence of nuclear PBR in different hepatic tumour cell lines with regard to binding to [3H] PK 11,195 and protein analysis. The results obtained by saturation binding experiments and Scatchard analysis of nuclear PBR density in parallel with the results on the growth curves of the cell lines tested, indicate that the nuclear PBR density correlates inversely with cell doubling time. Moreover, the cell line with high nuclear PBR proliferates in response to PBR ligands, whereas that with low nuclear PBR does not. All these findings support the idea that PBR could play a pivotal role in cell proliferation and this receptor protein could be potentially important either in early diagnosis or chemopreventive strategies against degenerative disease.