By Jennifer Carpenter
Science reporter, BBC News
In the UK, the recent rise in experiments is driven by GM animals
A new analysis claims the number of animals used worldwide in laboratory experiments is close to 115 million.
The annual figure is based on official statistics from 37 countries, but includes estimates for nations where data is unavailable.
The report hopes that better records will encourage more responsible policy-making and regulation.
Reported in the journal Alternatives to Laboratory Animals, the figure has been contested by pro-experiment groups.
The global estimate is the result of a joint venture between the British Union for the Abolition of Vivisection and the Dr Hadwen Trust for Humane Research.
They said it was the first estimate of global numbers of animals used in scientific research.
National statistics for many countries are not released, and so the UK-based team extrapolated national figures from the number of scientific papers that were published involving animals.
The research included animals that are used to maintain stocks, and also included animals deemed surplus and humanely killed.
In previous estimates, neither of these categories were included in national statistics.
"It is troubling that there are so many countries that appear not to record the lives of those animals suffering in their laboratories," said Wendy Higgins of the Trust.
"Knowing the number of animals used gives real ammunition for the general public to put pressure on their governments to play their part in the global reduction and replacement of animals in experiments," she told BBC News.
The results of the study estimate that the US and Japan use the greatest number of animals (17 million and 11 million, respectively), followed by Canada, France and Australia (all about 2.3 million).
Barbara Davies, communications director for the UK's Research Defence Society, argues that the study's final figure is inflated.
She said that the data for many countries was extremely limited, very variable and out of date.
"The paper makes too many assumptions and extrapolations to have any confidence in its conclusion," Ms Davies told BBC News.
"They know the media will pick up 115 million as the top-line result, and not delve deeper into how they achieved this number."
Ms Davies said the numbers needed to be put in context to show how society benefits from animal-testing.
In Britain, the number of animals used in laboratory experiments declined from a peak in 1970s, but since 1997 has shown a steady increased.
Official Home Office figures show a 6% year-on-year increase.
"This year is the first time in 16 years that we have seen the number of animals used in UK labs exceed three million," comments Ms Higgins.
The use of genetically modified animals - mainly mice - has more than quadrupled since 1995, and is responsible for the recent growth in the number of animals used.
Ms Davies said these animals were a powerful way to find out what a gene did, and how a flaw in it affected human health.
"The Human Genome Project threw up many new genes but we don't know what their functions are," she added.
By knocking out genes in animals, scientists hope to gain insight into the function of all the genes found by recent genome sequencing projects.
"It is in everyone's interest to replace animals in experiments wherever possible, but it is difficult, and that is why progress is slow," Ms Davies conceded.