The sexual transmission of HIV in gay couples can be stopped, a groundbreaking Australian study has shown.

In what has been described as "revolutionary" for gay people, the study proved the virus was no longer transmissible if the HIV-positive person had been properly treated.

The Opposites Attract study, conducted by UNSW Sydney's Kirby Institute, surveyed 343 couples where one man was HIV positive and the other HIV negative.

In each case, the HIV-positive partner had been treated to achieve an undetectable viral load.