Mathematical models can help to predict an organism's responses to varying levels of exposure to a particular substance. They can also help in improving the design of scientific experiments. These models are, however, no substitute for observation of the effects of a substance in a complex, living system. Computer data banks allow for the reduction of test duplication. But computers can only process and store existing knowledge, much of which has come from animal studies.
Animal testing is needed to expand that knowledge base.
Cells, tissues, and even whole organs obtained from animals and humans can be used for preliminary screening of chemical compounds. They can help identify substances that are so toxic that there is no purpose in continuing to investigate their potential use. However, in vitro tests cannot reveal the effects of a substance on a complex living organism composed of many different organs and systems. In the end, the validity of such tests must be verified by testing on an appropriate intact, living organism. However, because of their simple physiology, they shed little light on complex toxicity questions, and thus are less useful in late stages of testing protocols.