The long-tailed macaque is being threatened with extinction by a huge surge in international trade and the destruction of its habitat in Southeast Asia, conservationists said on Friday.
Species Survival Network (SSN), an international coalition of over 80 charities, says trade in the species had more than doubled in the second half of the last decade.
The group is pressing countries taking part in a meeting of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in Geneva this month to review the impact on the macaque of the trade.
"The long-tailed macaque is the most heavily-traded mammal currently listed on the CITES appendices and our research findings raise alarming questions concerning the long-term viability of targeted populations of the species if this trade is allowed to continued at current levels," Ian Redmond, chairman of the SSN Primate Working Group said in a statement.
Traders sold more than 260,000 long-tailed macaques - found mainly in Cambodia, Indonesia, Laos, the Philippines and Vietnam - between 2004 and 2008, a huge rise from the nearly 120,000 between 1999 and 2003.
The breeding and supply of the monkey has developed into a large scale business enterprise mainly in Southeast Asia with most exported for medical and scientific purposes.
Redmond said the population was also dwindling due to hunting, habitat loss and degradation, and human encroachment.
"There is also evidence of an illegal trade in wild-caught long-tailed macaques that is likely to have a significant impact on populations," he said.