Pope Benedict has said that condoms may be used in certain circumstances to reduce the risk of spreading AIDS.
He denied they were a real or moral solution to the spread of the disease but said they could improve the lives of some potential victims.
The Pope was responding to the charge that it was madness to forbid the use condoms where AIDS was widespread.
His remarks were made during an interview for a book which is due to be published next week.
He said that there might be a basis for making exception and cited the example of a male prostitute who, by deciding to use a condom, could be moving towards acknowledging that he could not do whatever he wanted to.
He said condoms were not a real or a moral solution to the evil of HIV infection.
One American theologian has interpreted the remarks to mean that homosexuals who use condoms to avoid harming another may eventually realise that sexual acts between members of the same sex are inherently harmful.
But Vatican watcher John Allen says the Pope is signalling that the use of condoms might be morally justified in limited cases, for example, that of a married heterosexual couple where one partner is HIV-positive and the other is not.
AIDS campaign groups have welcomed the Pope's statement.
The UN programme on HIV and AIDS said the Pope's comments were a significant and positive step forward.
