The Bill and Melinda Gates Foundation is pumping $500m into the Global Fund to Fight AIDS, Tuberculosis and Malaria - its biggest grant to the fund so far.
Gates, who is sacrificing day-to-day duties at Microsoft to lead his trust with wife Melinda, called the fund "one of the most important health initiatives in the world".
"We need to do everything we can to support its continued success, which will save millions of lives," Gates said in a statement.
The fund is projected to have a $2.1bn budget shortfall for the next two years. Founded four years ago, the fund has treated 544,000 people for HIV/AIDS, 1.4m for TB, and provided more than 11m bed nets to protect children from malaria.
The Gates Foundation will dole out its money in $100m parcels each year from 2006 to 2010, with the contributions for 2006 and 2007 supporting the fund's sixth round of financing. ®