"Science, in recent years, has made further progress in the determination of the death of a patient," the pope told a delegation of Catholic scientists and doctors.
"In an area like this, there cannot be the slightest hint of arbitrariness," the pontiff said, according to a text of his speech released by the Vatican.
He urged "the entire scientific community" to seek a new consensus on the end of life to assure "certainty for everyone."
Benedict's comments came two months after the Vatican newspaper Osservatore Romano published an article questioning whether brain death means the end of life.
The article highlighted cases of pregnant women in irreversible comas who have been kept alive so as to allow their babies to be born.
"The idea that a person ceases to exist when the brain no longer works... directly contradicts the concept of a person according to Catholic doctrine and the directives of the Church on the issue of persistent comas," the author wrote.
Although Osservatore Romano is a Vatican publication, it does not reflect official changes in doctrine.
Vatican spokesman Federico Lombardi said that while the article was "a weighty and interesting contribution... (it) cannot be considered as a position" of the Catholic Church.
Benedict also reiterated Friday his opposition to "the creation and destruction of human embryos for medical purposes" and called the trafficking of human organs "abominable."