This is taken from a school essay I wrote for Philosophy and Ethics. I don't necessarily support animal testing, before the Animal Liberation Front gets any ideas...
Many anti-vivisection campaigners like to wave around the “fact” that vivisection and animal research has accomplished nothing whatsoever, and use it often in campaign literature. However, when one looks at the statistics, it is obvious that it is not the case.

For a start, animal research is inexpensive compared to other forms of research. For every pound spent on medical research, five pence is spent on animal research. Also, if it is cruel to use animals in this way, what about the two million cats and dogs abandoned each year (including the two hundred a day handled by the RSPCA) and the eight hundred million animals slaughtered for our consumption, such as cows, pigs, chickens and turkeys. The 2.6 million animals used each year in medical research pales in comparison to these millions of animals. The industry is very tightly regulated, and as such the animals are treated with the utmost care.

We need to be able to evaluate the effects of new drugs and treatments in a living body, as there is no computer simulation which can simulate the complex body systems of a living being, and testing on humans would be seen and incredibly unethical.

Many of our cancer treatments, which save hundreds, even thousands of people a year, such as radiotherapy (using targeted gamma rays to kill rapidly dividing cells such as the cancerous cells in the tumour) and chemotherapy (using drugs for the same purpose) were first developed and proven with animal research.

Many tools to treat coronary heart disease, such as the heart/lung machine, the coronary bypass operation, the pacemaker and beta-blocking drugs (which reduce blood pressure and stave off heart attacks) were first tested on animals, and now save thousands of lives every year.

This shows that animal research saves thousands, maybe millions of lives each and every year.