Bion 2 was a Bion satellite launched by the Soviet Union on October 22, 1974 at 1800 hours UTC. It carried albino rats for biomedical research. Soviet, Czechoslovak, and Romanian scientists subjected the rats to daily radiation doses from a gamma source by ground command. When they were recovered 20.5 days later, many rats had developed lung problems and their blood and bone marrow had changed more than those of control specimens. It had an on-orbit dry mass of 5500 kilograms and had a US National Space Science Data Centre ID of 1974-080A.
The spacecraft was based on the Zenit spy satellite with emphasis on studying the problems of radiation effects on human beings.
It was also known as Biocosmos 2, Cosmos 690 and 07478