The mechanisms regulating the activity of telomerase, predominantly human telomerase, are con sidered in brief. The localization of telomerase complex components in the cell is described, and telomerase activities unrelated to telomere elongation are discussed. Human diseases that correlate with reduced telomerase activity, short telomeres, and rapid telomere shortening are overviewed. The possibilities to activate transcription of exogenous hTERT by various natural and synthetic compounds are described along with the effects of cell transfection with active hTERT. Exogenous hTERT activation increases the cell proliferation potential and may be employed in cell therapy. It is emphasized that elevated hTERT expression may cause cell malignant transformation, especially in the case of hTERT transfection. This possibility must be considered when choosing the means of telomerase activation for therapeutic purposes.