Basing on the assumption of damage accumulation as the primary cause of cell ageing the mechanisms of such damage and corresponding defense, systems in cyanga, bacteria (bliie-green algae.) are analysed in terms of comparison with those in mama- lian cells currently used in cytogerontology. It is rather possible that chanisnr of macromolecular damage during «light ageing» of cyanobacteria is pnotooxi- dation in contrast to free radical damage as the putative mechanism of «Stationary phase ageing» as well as in vivo ageing of mammalian cells. Nevertheless free radical processes also take place in cyanobacteria and play their, own role in primary cell damage. As a result, there exist some peculiarities of cyanobacteria defense systems. Since authors believe that it is cell proliferation slowing down, that induces the damage accumulation and cell ageing, two available in literature mathematical models describing the general slowing down of cell proliferation due to intrrinsic mechanisms for eucaryotic (human diploid) and cyanobacteria cells in culture are compared. The basic assumptions of the models and the growth kinetics regularities predicted by them appear to be close enough.. Thus it is assumed that the mechanisms responsible for the slowing down of cell. proliferation and therefore cellular senescence in mammalian cells and in cyanobacteria are very similar. All items discussed in the part 3 review allowed to consider cyanobacteria culture as very useful tool for comparative and evolutionary cytogerontology studies.