VATICAN CITY (AP)--For the second time in a few days, Pope John Paul II, struggled with health problems and let a cardinal take his place in a major Holy Week ceremony Thursday.
The pope read the homily and recited or chanted several prayers, but Cardinal Dario Castrillon Hoyos took the pontiff's customary place at the main altar of St. Peter's Basilica to celebrate the Mass in which priests renewed their vows.
Four days earlier, breaking his tradition, John Paul ceded his place at the altar for Palm Sunday Mass, the ceremony that opens Holy Week, the most important stretch on the Church calendar.
The pope was scheduled to participate later Thursday in another lengthy ceremony, a symbolic washing of priests' feet, in a Rome basilica.
The Vatican hasn't officially said why the pope has made the changes but in recent weeks it has said doctors have insisted that the pope rest a bad knee, afflicted with arthrosis, a joint disease.
The pope, who will be 82 in May, has been long plagued with health problems.
Symptoms of Parkinson's were evident in Thursday morning's ceremony in St. Peter's. The pope's hands trembled badly as he clasped them together, and his speech was often slurred.
There has been much concern in the Vatican and among the faithful at large about how John Paul will weather the rest of Holy Week. Besides the two ceremonies on Thursday, there is a prayer service Friday night at the Colosseum to commemorate Jesus' suffering before his crucifixion.
Then he marks Easter with a Saturday night vigil service in St. Peter's Basilica and leads Mass in St. Peter's Square on Easter Sunday.
During Thursday morning's ceremony, hundreds of priests in simple white cassocks renewed the vows they made when they joined the priesthood.
Last week, John Paul broke his silence on the sexual abuse scandals involving priests that have rocked dioceses in the United States and elsewhere. He said the ``grave scandal'' had cast a ``dark shadow of suspicion'' on other priests who are serving the Church well.
The Thursday morning ceremony had just ended when the latest high-level resignation came in the current scandal. The archbishop of Poznan in John Paul's native Poland said that the pope had accepted his resignation following newspaper allegations that he made homosexual advances on young clerics.
John Paul in his homily Thursday morning invited prayers for ``our brothers who didn't meet their commitments that came with priestly ordination or who are going through a period of difficulty and crisis.''
While thanking God for the gift of the priesthood, John Paul said, ``we cannot help but confess our infidelities.''