The number of animal experiments in the UK has reached its highest level in 25 years, government figures show.
Over 3.7 million scientific experiments on animals were carried out in 2010 - that's 105,000 more than in 2009.
It's largely because of an increase in breeding mice and fish to produce genetically modified (GM) and mutant animals, that have genetic defects.
But it's angered campaigners who say new European guidelines threaten welfare standards for UK lab animals.
When GM animals are excluded from the statistics, the total number of experiments rose by 18,000, to 2.1 million.
As for why the experiments were carried out, there was a drop in the number for safety testing, but more universities carried out animal experiments, and there were also increases in procedures looking at diseases like cancer.
Campaigners and animal charities like the RSPCA are now challenging the government to prove that it's committed to reducing the number of experiments carried out on animals.
That's because they say some of the new European regulations aren't as good as those already in place in the UK.