A key fund that funds the fight against AIDS, tuberculosis and malaria is looking for new investments of £ 11 billion.
French President Emmanuel Macron is launching the last round to replenish the global fund in Paris.
It is called "a decisive moment".
The fund says progress has slowed due to the tremendous political engagement and increase in insecticides and drug resistance.
Increasing the target amount could help save 16 million lives, it is claimed, as well as halving the mortality rate from these three significant diseases.
The £ 11 billion ($ 14 billion) would be spent on the medicine that treats and prevents the transmission of HIV, the drugs against tuberculosis and the nets to protect themselves from malaria.
"Progress has stopped"
The executive director of the fund, Peter Sands, told BBC News: "We have made extraordinary progress in reducing these deaths, but progress has stopped.
"Entering a new post, I was really impressed by the strength of political support for the Global Fund in many different capitals.
"I am not at all satisfied with the challenge of collecting the money we need – and of course the geopolitical environment is complicated.
"But we are confident of having a strong investment and a demonstrable level of impact," he said.
The Global Fund has generally been considered a success story in the way it collects and uses global health funds from governments and other donors.
But the investment case warns against funding shortfalls and states that this could threaten the third goal of sustainable development, an internationally agreed goal to end disease epidemics and create resilient health systems for all people.
"New threat of infections"
Cases of malaria are increasing, after years of constant decline. Two-thirds of all malaria deaths affect children under the age of five.
And although anti-retroviral drugs have stopped millions of people dying of AIDS, the massive increase in young populations in Africa poses a threat to new infections rather than to the height of the epidemic at the start of this century.
Tuberculosis kills more people than any other infectious disease – and drug resistance cases make up a third of all deaths worldwide due to antimicrobial resistance.
The Director-General of the World Health Organization, Dr. Tedros Adhanom Ghebreyesus, paid tribute to the "truly impressive growth" of the Global Fund during its 17 years.