Laboratory mice. Cages of laboratory mice undergoing experimentation. Experiments are distinguished by blue labels on each cage. Laboratory mice are the most-commonly used animals for biological and medical experiments. Such research is either to test the safety of non-medical substances (such as cosmetics or pesticides) or medical experiments to test for the effects of new drugs. Animal experimentation is controversial and alternatives are being developed. However, many animal experiments remain compulsory by law before new products can be released.