Gay and lesbian activists and some Anglican priests have reacted angrily after Pope Benedict XVI said mankind needed to be saved from a destructive blurring of gender.
In a speech to Vatican leaders, Pope Benedict said that saving humanity from homosexual or transsexual behaviour was as important as protecting the environment.
The United Kingdom's Lesbian and Gay Christian Movement said the comments were "irresponsible and unacceptable".
Vladimir Luxuria, a transgender former Italian MP, called his words "hurtful".
The row erupted as news emerged that the pontiff is to pay his first visit to the Holy Land in May next year.
Pope Benedict made the comments in an end-of-year speech. Defending God's creation was not limited to saving the environment, he said, but also about protecting man from himself.
In the speech, the Pope criticised gender theory, which gay and transsexual groups promote as a key to understanding and tolerance.
Gender theory, which originated in the United States, explores sexual orientation, the roles assigned by society to individuals according to their gender, and the ways in which people perceive their own biological identity.