The action of Röntgen ionizing radiations (from 1,000 r to 120,000 r) was experimented on the migration and the survival of «in vitro» hanging drop cultivated chicken fibroblasts. Radial migration area was decreased with the growing of radiation doses. This action was immediate for 120,000 r but it showed an increasing days latency for smaller doses. Culture survival lasted 6-9 days after doses ranging from 120,000 r to 20,000 r whereas at 10,000 r and 5,000 r it was of 20-25 days. A 1,000 r reduced temporarily migration speed which went back to normality 15 days after irradiation. These cultures survive indefinitely.