To count the dead they ride motorbikes, charter planes and wade through snake-infested rivers.
The precious statistic can help aid agencies convince a weary world there is a crisis in the jungles of Africa or forgotten corners of Iraq - where death comes from hunger and disease related to war as well as from war itself.
"There's a humanitarian crisis in Congo, (but) we need data to show there's a problem," said Richard Brennan of aid agency International Rescue Committee (IRC).
Its latest survey in the central African state found 45,000 people a month were dying from war-related hunger and disease, even though the conflict there had ended officially in 2003.
But pinning down precise, and credible, numbers is difficult and often intensely political. To prove its point, the IRC and other agencies have to go to where the dead are.
"It was really difficult to reach some places...We chartered airplanes and boats. We hired motorbikes," Brennan said.
One team came to a riverbank in Congo where the bridge had been washed away and waded across with a precious laptop perched on a team member's head. Villagers, heaving their motorbikes over the waist-high brown water, told them to watch out for snakes.
Other IRC teams visited communities living next to rubbish dumps the size of two-storey houses, and were given piggyback rides across open sewers to ask their questions about births and deaths.
Based on this arduous field work in a random sample of 14,000 households in every province in the country -- and Congo is the size of western Europe -- the IRC calculates the war dead since 1998 at 5.4 million; citing this as the deadliest conflict since World War Two.
The effort to provide scientifically grounded death tolls - calculating the death rate and comparing it to the regional norm - has boosted donations to help Congo recover from a conflict that sucked in seven nations and enveloped the region.
DEATH TOLLS IN IRAQ
The Congo surveys haven't been particularly controversial, but researchers trying to pin down a death toll for Iraq know their findings will come under intense scrutiny.
"People who oppose the war usually cite the highest death toll they can find, and people in favour of it tend to cite the lowest," said John Sloboda, who co-founded Iraq Body Count to collate reports from the media and mortuaries.
