We investigated whether the telomere length, i.e. mean terminal restriction fragment (TRF) length, decreases during in situ aging in normal human oral fibroblasts (NHOF). For this purpose, NHOF cultures were established from 50 different donors and tested after 14 population doublings (PD) when the cells were replicating exponentially. Telomere-specific Southern blotting and digital quantitation showed that the mean (+/-standard error (S.E.)) TRF length of all tested cultures was 7.72+/-0.17 kbps. The plot of TRF mean length versus donor age showed high variability in individual length with an apparent average decline of -7.8 bp per year of age, which was not statistically significant (r=0.11; P>0.1). These data indicate that telomere shortening does not occur during donor aging in situ, and therefore, is not physiologically relevant for NHOF.