Animal rights activists have published shocking pictures and video of hundreds of monkeys they claim were killed because they were too big for testing in British laboratories.
The disturbing images show discarded dead monkeys stacked in piles on the floor or dumped in rubbish bins.
Mutilated bodies can also be seen in a skip awaiting incineration, according to the British Union for the Abolition of Vivisection.
The group claims the unwanted healthy primates were given lethal injections in the heart and then burned on a monkey-breeding farm on the holiday island of Mauritius.
British firms are said to pay £260 a time for the animals but overseas labs are said to only be interested in those weighing less than 3.5kg.
BUAV claims pregnant monkeys and babies are also being slaughtered at the Noveprim breeding farm, a major exporter of as many as 10,000 moneys a year to the UK, Spain and the USA.
BUAV Director Sarah Kite last night called on the British government to order an immediate ban on the import of monkeys from the Indian Ocean island.
This is a cruel and senseless slaughter, she said. It is unacceptable that monkeys who have been exploited for years are now simply discarded because they are of no further use to this company.
These monkeys should be released into the wild so that they can live out the rest of their lives freely. By importing monkeys from this company, the UK is perpetuating this appalling cruelty, she added.
Mauritius is the worlds second-largest exporter of long-tailed macaques for research.
Three-quarters of the monkeys are used for toxicology tests on new drugs. The others are tested in studies for conditions such as Parkinsons disease, Alzheimers and Aids.
In 2011, 518 monkeys were exported to the UK from Mauritius. The previous year, the number was even higher at 1,059. Only America bought more.
BUAV said it believes the killings started at the beginning of October and will continue until the end of next month.
A Noveprim spokesman wasnt available for comment last night.