Why modification of the LD50 test will not be enough

During the last 10 years, the 'Three Rs' (reduction, refinement and replacement) concept of alternatives has come to be widely accepted, and new national and international laws require that non-animal procedures should replace animal experimentation wherever possible. Some reduction and refinement of animal use in toxicity testing has been achieved, and non-animal methods are becoming widely used as prescreens. However, even replacing the LD50 test by a modified and validated animal test, the Fixed Dose Procedure, will be a major achievement. In this paper it is argued that this is not good enough, and that more effort must be put into the development, validation, acceptance and use of genuine replacement alternative tests.