Using condoms may sometimes be justified to stop the spread of AIDS, Pope Benedict says in a new book, in a major shift that relaxes one of the Vatican's most controversial positions on their use to combat the disease.
The pope's words in the book to be published on Tuesday - while limited in scope and which do not change the Catholic ban on contraception - were nonetheless greeted as a breakthrough by dissident Catholics, AIDS workers and commentators.
"It is a marvellous victory for common sense and reason, a major step forward towards recognising that condom use can play a vital role in reducing the future impact of the HIV pandemic, said Jon O'Brien, head of the US group Catholics for Choice.
In the 219-page book, Light of the World, the pope also speaks frankly about the possibility that he could resign for health reasons and defends wartime pontiff Pius XII against Jewish accusations that he turned a blind eye to the Holocaust.
He says scandals of sexual abuse of minors by priests. were "an unprecedented shock", even though he had followed the issue for years, and says he can understand why people might quit the Church in protest.
But it is the section on condoms in the book - a long interview with German Catholic journalist Peter Seewald - that marked a crack in the once tightly shut door of Church policy.