When animal rights groups protest the use of animals in experiments, one of their favorite targets is a test known as the LD50. Since the late 1920's, scientists have killed millions of animals to conduct the test, which was designed to help judge the acute toxicity of drugs, pesticides, and other chemicals. But animal rights groups and scientists in general agree that the test is now outdated and has limited value. Even so, according to animal rights activists, industry continues to perform the test to meet federal requirements, unnecessarily killing millions of animals a year. The animal rights groups have raised such a ruckus that last month 16 congressmen wrote a joint letter to several federal regulatory agencies expressing concern about the test. About the same time, the Food and Drug Administration, with several other agencies, hosted a daylong workshop on the topic, which revealed that there is considerable confusion about how often the test is actually used and about federal requirements concerning the test.
Sun, M. (1983). Lots of talk about LD50. Science, 222(4628), 1106-1106.