Laboratory mice. A laboratory mouse being transferred to a cage by the gloved hand of a researcher. 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 effect of new drugs. Animals have also been used to produce vaccines and hormones such as insulin. Animal experimentation is controversial and alternatives are being developed. However, many animal experiments remain compulsory by law before new products can be released.