A new type of HIV drug, designed for people who are resistant to other treatments, has been approved by the US authorities.
Roche, the makers of Fuzeon are confident it will also win European approval within weeks.
Fuzeon is the first of a new class of drugs known as fusion inhibitors.
It is designed to combat the growing problem of resistance to older HIV drugs.
However, the drug is likely to be very expensive - around $20,000 a year.
This drug will extend treatment options for people who are in dire need
And it is predicted that as few as 12,000 people world-wide will get the drug by the end of this year.
Fuzeon, also known as T-20, has been eagerly awaited because it is the first real alternative treatment in seven years for Aids patients running out of options.
Unlike existing drugs that work inside the cell, Fuzeon blocks HIV from entering healthy human immune cells.
Research published on the New England Journal of Medicine website found that HIV patients who took Fuzeon were twice as likely to achieve undetectable levels of HIV in their blood than those who did not take the drug.
The drug was also able to suppress HIV levels in patients who had previously developed resistance to other drugs.
US Health and Human Services Secretary Tommy Thompson said on Friday: "The accelerated approval of this new drug should provide new hope for those suffering from advanced HIV infection."
At present there is still no cure for HIV, which has killed 28 million people worldwide and infected 40 million more.
A combination of drugs can keep Aids at bay for years.
However, HIV is able to mutate, and to build up resistance.
Thus, current HIV drugs often tend only to be effective for a limited period of time.
Roche officials have said they do not expect Fuzeon to be suitable for use in Africa - the epicentre of the global Aids epidemic - given the high cost and complexity of production.
However, most African patients have not yet developed resistance to existing drugs.
The US Food and Drug Administration approved the use of Fuzeon with other anti-HIV drugs to treat advanced HIV infections in adults and children age 6 and older.
Michael Carter, of the UK National Aids Manual, told BBC News Online "This drug will extend treatment options for people who are in dire need.
"Let's hope that it is made available to them."
His comments were echoed by Derek Bodell, chief executive of the National AIDS Trust.
He said: "The advent of these new treatments have brought new hope to people who have exhausted other treatment options.
"It highlights that whilst there is still no cure for HIV, medical and scientific research is still offering longer and healthier lives for those fortunate enough to have access to them."