More than 1,100 men in New South Wales have signed up to trial a new preventative HIV drug, which doctors say may help dramatically decrease the number of infections.

The Kirby Institute's trial, which aims to recruit 3,700 men, involves participants taking pre-exposure prophylaxis (PREP), a drug which prevents HIV infection.

PREP is yet to be listed on the Pharmaceutical Benefits Scheme but the Therapeutic Goods Administration recently licensed one brand, Truvada.

Professor Sharon Lewin of Melbourne's Doherty Institute said she hoped the NSW trial would help the drug become more accessible to Australians.

"The benefits are absolutely huge," she said.

"In other countries, particularly in the US, they've demonstrated that as you introduce Truvada for prevention they've seen a dramatic reduction in new HIV infections.

"We still have 1,000 new HIV infections a year in Australia and we would be hoping to see a dramatic decrease in that number."

Professor Lewin said she hoped the listing would lead to the drug becoming more affordable.

"The big hope is [for] PBS, our funding body, to subsidise these drugs and that could have a very, very significant impact on the epidemic," she said.

"If you were to buy it as an individual it would cost $800 to $1,000 per month, however it is also possible to get these drugs in what we call generic form meaning that they're made by a different manufacturer and those could be much cheaper, around $2 per day."

Professor Lewin, who has no affiliation with Truvada but has received grants from Truvada's maker, Gilead, to research Hepatitis B, said the drug would be cheaper when it goes off patent in a year or two.

She said cheaper versions of the drugs had already been imported by people who had bought them online.