A new survey shows lemurs are far more threatened than previously thought.
A group of specialists is in Madagascar - the only place where lemurs are found in the wild - to systematically assess the animals and decide where they sit on the Red List of Threatened Species.
More than 90% of the 103 species should be on the Red List, they say.
Since a coup in 2009, conservation groups have repeatedly found evidence of illegal logging, and hunting of lemurs has emerged as a new threat.
The assessment, conducted by the Primate Specialist Group of the International Union for the Conservation of Nature (IUCN), concludes that 23 lemurs qualify as Critically Endangered - the highest class of threat.
Fifty-two are in the Endangered classification, and a further 19 Vulnerable to extinction.
"That means that 91% of of all lemurs are assessed as being in one of the Red List threatened categories, which is far and away the largest proportion of any group of mammals," said Russ Mittermeier, chairman of the specialist group and president of Conservation International.
Species can qualify for a Red List category on several measures.
A Critically Endangered listing can mean the population numbers less than 50 mature adults or that it has shrunk by 80% over 10 years, for example.
The previous lemur assessment, published in 2008, put eight species in the Critically Endangered class. Eighteen were Endangered, and 14 Vulnerable.
The new assessment also confirms that there are more lemur species that previously thought.
Detailed observation and genetic testing have revealed several cases where populations that had been presumed to belong to one species were in fact from different ones.
The 103rd species, a mouse lemur that has yet to be named, was identified during the assessment exercise.
But the experts have been dismayed by ongoing deforestation, and have documented hunting of lemurs at levels not seen before.
"Several national parks have been invaded, but of greater concern is the breakdown in control and enforcement," Dr Mittermeier told BBC News.
"There's just no government enforcement capacity, so forests are being invaded for timber, and inevitably that brings hunting as well."
Christoph Schwitzer, head of research at the UK's Bristol Zoo, said his students had seen this at first hand in the northwest of the island.
The zoo runs a conservation project there with blue-eyed black lemurs (Eulemur flavifrons) and Sahamalaza sportive lemurs (Lepilemur sahamalazensis) - both Critically Endangered species.
"I used to be very optimistic, I thought the project was really going somewhere and the local communities were on our side," he said.
"But from 2009 onwards, it just deteriorated markedly. Now we see local people hunting lemurs, even blue-eyed black and sportive lemurs which we never saw before.
"In previous years, when you had students working in a forest fragment, you could be certain there would be no illegal acts going on because they knew we'd report them.
"Now, my assistants find people doing illegal logging and they don't care, they just carry on and it doesn't matter because there's no law enforcement."
Andry Rajoelina, who seized power in the 2009 coup, has pledged to hold elections "as soon as possible". Several scheduled election dates have already come and gone.
About 90% of Madagascar's original forest has been lost, with lemurs and the many other endemic forest-dwelling species clinging to an increasingly precarious existence in the fragments that remain.
Hardwood trees such as ebony, rosewood and pallisander are particularly prized.
Two years ago, environmental campaigners found beds made of Madagascan hardwood on sale in Beijing for more than $1m.
Most of the Madagascan population lives on less than $2 per day.
The new assessments will sent out for review by other experts. When confirmed, they will form part of the next global Red List, probably published next year.