[en] The term radiation hormesis is used to describe unexpected positive biological effects after very low doses of ionizing radiation. In rodents, these effects include slight increases in median life span and increased body weight. Accelerated germination of seeds and increased plant growth also occur. In bacteria, a reported optimal growth occurs when the bacteria receive 0.05 to 0.1 Gy/h (5 to 10 rad/h). Reduced growth of bacteria has been attributed to an ionizing radiation deficiency. Many radiation biologists assume that these effects of low-level irradiation are based on excess repair or adaptation to minimal injury. Another thesis is that a direct stimulation of growth is produced by minimal ionizing radiation. Some investigators even theorize that radiation is essential for life. In toxicology and pharmacology, similar stimulation of biological systems by sublethal and minimal doses of poisonous substances has been known for many years as the Arndt-Schulz Law or Hueppe Rule. This overview includes the opinions on radiation hormesis of speakers at the Conference on Radiation Hormesis held in Oakland, California, in 1985. 23 references