The LD50 test.

The nature of the LD50 test and its central place in the conceptual development of pharmacology is reviewed. The results of the test and possible uses are outlined. Some guidelines are set out for the development of alternatives to LD50 tests. Some circumstances are suggested in which it seems likely that some form of the test will continue to be required. It is concluded that the problem of replacing the LD50 test with apparently more elegant methods is part of the larger and more fundamental problem of bringing science to the study and regulation of toxicology.