Millions of animals are used every year to do many different types of researches; such as, medical, cosmetics, environmental or biochemical research. Animals are used in test new types of drugs, pesticides or commercial products that are meant to be used in humans. However, there are many controversial problems about this type of research because the effects on the animals and the minimum successful results. There are many reasons for why animal models should be replaced by other alternative in research. To begin with, the used of animal models for research is something that is have been done since BC. There is data of the dissection of live animals that have been found in ancient Greek writings; consequently, many physician-scientists of the time experimented with living animals and make many discoveries that helped to improve the knowledge of humans, but at this time, it was thought that animals were not able to feel any pain. “Aristotle believed that animals lacked intelligence, and so the notions of justice and injustice did not apply to them. Theophrastus, a successor to Aristotle, disagreed, objecting to the vivisection of animals on the grounds that, like humans, they can feel pain, and causing pain to animals was an affront to the gods.” As the time passed, there were more people that started to get concerned with this practice and by the 19th century, the Society for the Protection of Animals Liable to Vivisection was created in 1875, followed by the formation of similar groups. I have to agree with the many contributions that animal experimentation has made for humans, but I believe that was acceptable hundred years ago when nothing was known about our body and our systems. As a human, I would rather experimented in an animal than a family member, but nowadays, we are conscious that humans can differ in many ways from animals; moreover, I think animals have helped with everything they got, and I do not think we are goi