Research

• Medicines and chemicals need to be tested to assess the effects on humans. This is a vital part of any testing, but especially so in drug research. It would be incredibly dangerous to skip this part of testing and move straight to giving new medications to humans in case there were some dangerous side effects. Chemicals and solvents also need to be tested to ascertain their toxicities, so safety levels can be calculated.
  
  

Genetic Similarity

• The reason mice have become so popular for use in scientific experiments is because they are genetically very similar to humans. This is vital, as testing on animals that share fewer similarities with humans will give inaccurate results. This genetic similarity is especially important in medical research, as genes can be removed form mice to encourage certain ailments and cancerous cells can be easily introduced into the body.
  
  

Convenience

• Mice are cheap, easy to care for and can be easily bred. There are other animals that are also genetically similar to humans --- for example, pigs are more accurate in terms of size, which is why pig hearts are sometimes used for transplants. Mice take up less space, cost very little to feed and breed more rapidly. It is also kinder to use mice than to use other animals, as mice like to live in large groups, which is how they are stored pre-experimentation.
  
  

Legality

• The Animal Welfare Act of 1985, also called the The Improved Standards for Laboratory Animals Act, set out strict guidelines on how laboratory animals should be treated. It set forth provisions for how long dogs needed to be walked each day and rules regarding the psychological well-being of nonhuman primates. This meant that mice were much easier to care for before and during experimentation compared to other animals, due to enclosure sizes and exercise regimes.