An experimental Ebola drug, ZMapp, has cured all 18 of the laboratory monkeys infected with the deadly virus.
According to Reuters, these include those suffering the fever and hemorrhaging characteristics of the disease and had been hours from death.
Monkeys not treated until five days after infection also survived.
Reportedly, no other experimental Ebola therapy has shown such success in primates. Five days of infection in the animals has been said to be the equivalent of nine to 11 days after infection in humans.
Although, two American aid workers who contracted Ebola in Liberia were cured after receiving ZMapp, their physicians do not know if the drug helped.
A Liberian doctor with the disease on Monday was confirmed dead, despite being given the drug, as did a Spanish priest.
ZMapp, produced by Mapp Biopharmaceutical in San Diego, USA, has never been scientifically tested in people, and the current study was the first in primates.
The development was described by virologist Thomas Geisbert of the University of Texas Medical Branch as a monumental achievement.
There are no approved Ebola vaccines or treatments, but human safety trials will begin this week on a vaccine from GlaxoSmithKline, and later on, on one from NewLink Genetics Corp.
According to the World Health Organisation, the Ebola outbreak in West Africa has killed 1,552 people out of 3,069 confirmed cases and is on pace to infect 20,000. WHO also said the outbreak would almost certainly continue into 2015.
ZMapp has been described as a mix of three antibodies that bind to proteins on Ebola viruses and trigger the immune system to destroy them.