Telomerase is a ribonucleoprotein enzyme specialized in telomere elongation which may be involved in the control of cell proliferation, and consequently could play a role in oncogenesis, 1997 was a very exciting year for telomerase understanding. First, the sequence of the human telomerase catalytic subunit revealed strong homologies with known reverse transcriptases. Second, the production of viable mice deleted for the RNA moiety of the enzyme showed that telomerase is essential to maintain telomere length in germ cells but is not required for tumour formation.