New research suggests circumcision could be effective in preventing the spread of HIV among men.
Foreskin cells are thought to be more susceptible to HIV
The study of more than 3,000 men in South Africa was done by the French agency for Aids and Viral Hepatitis.
The data, outlined at a conference in Brazil, shows male circumcision prevented about seven of 10 infections.
UN health agencies have cautioned that more trials are necessary before they will recommend this as a method to protect against Aids.
Previous studies have suggested that men who are circumcised have a lower rate of HIV infection.
It is thought that the cells of the foreskin are much more susceptible to HIV than cells on other parts of the penis, so by removing the foreskin, the likelihood of infection drops.
Further trials are being carried out in Uganda and Kenya to measure the effect of circumcision on other populations.
If similar results are found, then circumcision could be used alongside condoms to prevent the spread of HIV, the BBC's Ania Lichtarowicz reports from the conference in Rio de Janeiro.
But implementing this measure on a large scale will be complicated, our correspondent says.
She says that ensuring safe techniques and changing cultural and social attitudes towards male circumcision will prove challenging.