During an open air mass on Sunday at a shrine to Mary, the highlight of his visit to the French town, he struggled as he spoke against abortion and euthanasia, making a special appeal to women.
"To you women, falls the task of being sentinels of the invisible," he told about 300,000 pilgrims.
"I urgently appeal to all of you, dear brothers and sisters, to do everything in your power to ensure that life, each and every life, will be respected from conception to its natural end.
"Life is a sacred gift, and no one can presume to be its master," he added.
But the 84-year-old pontiff dropped some paragraphs from his prepared message and faltered through a lengthy address in midday temperatures which reached 30C.
"Help me," he whispered in Polish during his message as he gestured to aide Monsignor Mieczyslaw Mokrzycki for a glass of water. "I must continue."
About 300,000 pilgrims, many in
wheelchairs, attended the mass
The multi-national crowd erupted into applause, many moved to tears at his refusal to yield to the pain of his Parkinson's disease, which was very evident during the visit - the 104th of his pontificate.
The pontiff, together with more than a thousand clergy, was celebrating the Feast of the Assumption, when the Virgin Mary - the mother of Jesus Christ - was taken up into heaven at the end of her earthly life, Catholics believe.
Confined to a wheelchair, like many of the pilgrims, the pope displayed worrying signs of his poor health throughout his trip.
He tired quickly and at one stage alarmed aides when he stumbled while kneeling.
"Life is a sacred gift, and no one can presume to be its master"
Pope John Paul II
Many pilgrims have expressed fears that this may be his last foreign visit.
He has been invited to attend an Orthodox Church
celebration in Istanbul in November and to Ireland next year.
But the Vatican, holding to its usual caution, has not confirmed any further foreign travel for him.