Telomere shortening in human liver with aging and chronic inflammation was examined by hybridization protection assay using telomere and Alu probes. The reduction rate of telomere repeats in normal liver (23 samples from patients 17-81 years old) was 120 bp per year, which is in good agreement with the reported reduction rate in fibroblasts of 50-150 bp at each cell division and replacement rate of human liver cells, once a year. Mean telomere repeat length shortened to about 10 kbp in normal livers from 80-year-old individuals. The number of telomere repeats in chronic hepatitis (26 samples) and liver cirrhosis (11 samples) was significantly lower than that in normal liver of the same age (P < 0. 01). Telomere length in all these chronic liver disease samples, other than two exceptions, was not reduced shorter than 5 kbp, which was assumed to give a limit of proliferation (Hayflick's limit) to untransformed cells.