Preparations from deer antlers are well known by their multiple medicinal properties. In particular, their health-giving effect on senescing organism has been repeatedly shown. In the study we investigated effect of water extract of reindeer mature antler powder (ERAP) on the kinetics of growth and "stationary phase aging" of HeLa (clone 11) cell line. Cell suspension was placed in the wells of 24-well plastic tissue culture plates with seeding density of 15 10(3)/cm2. The growth medium contained ERAP at 0, 10 or 100 microl/ml. In every 1-3 days microscopic evaluation of live cell number in the wells has been made. It turned out, that ERAP at 10 microl/ml increased proliferation rate of HeLa cells as well as their saturation density, i.e. acted as a geroprotector. The result was also confirmed by the observed "stationary phase aging" slowing down leading to increase of the "average life span" of cell culture. However, effect of ERAP at 100 microl/ml was different. In that case the evident decrease of cell culture saturation density was observed indicating increase of the culture "biological age". Besides, the cell death began earlier leading to decrease of the "average life span" of the cell culture. We think that ERAP contains some compounds with geroprotector activity as well as some geropromoters, or cell proliferation inhibitors. At the lower ERAP concentration in growth medium content of geropromoter(s) is too low for its effect manifestation and the evident "rejuvenation" of the cell culture is observed. At the higher concentration of ERAP (100 microl/ml) the content of geropromoter(s) reaches the "working" value and this not only masks the effect of geroprotector(s) but also leads to the cell culture "senescence".