Apoptosis plays a central role in the homeostasis of the immune system. During aging, there is an altered regulation of pivotal molecules that are responsible for the regulation of this type of cell death, such as those of the Fas/FasL system. Understanding the regulation of these genes can help to clarify, at least in part, the age-related changes that occur in immune cells. We have developed an original real time PCR assay for quantification of mRNA for Fas and FasL, and have studied a group of young donors, middle aged subjects and centenarians. We have found that the production of Fas mRNA is greatly increased in resting lymphocytes from centenarians; such an increase follows an age-related trend. On the contrary, the production of mRNA for the molecule, which is the natural ligand of Fas, i.e. FasL, is consistently reduced. Our preliminary results suggest that during aging a subtle balance in the production of molecules that cause apoptosis could exist, and that, in order to avoid an excessive death of immune cells, a still unknown mechanism could compensate the increase of Fas with the reduction of FasL.