Pope John Paul II, recovering from flu in hospital, has missed Ash Wednesday services at the Vatican for the first time in his 26 years as pontiff.
The Pope has his own chapel in the hospital
US Cardinal James Stafford presided at services on the Pope's behalf.
The Pope has spent the last nine days at Rome's Gemelli hospital - making just one appearance on Sunday to give his regular blessing to pilgrims.
But a Vatican spokesman has raised hopes that the 84-year-old pontiff will soon be able to leave hospital.
Joaquin Navarro-Valls said he hoped Thursday's update on the Pope's health would be the last before he is discharged.
"I can confirm that tomorrow at midday there were will be another bulletin, and I hope it will be the last," he said.
Pope John Paul II marked Ash Wednesday - the first day of Lent - in his hospital room, receiving ashes he had earlier blessed.
Like Catholics around the world, he had his forehead marked with the sign of the cross in ash.
The head of the Italian bishops' conference, Cardinal Camillo Ruini, said he had visited the Pope in hospital on Wednesday.
He said he had found the pontiff to be "truly in good shape".
Ash symbolises mortality at start of 40-day abstinence
Continues until Easter, chief feast in Christian calendar when believers celebrate Christ's resurrection
Other Christians, including Anglicans, observe Ash Wednesday
Many believers hold fasts or forego pleasures during Lent
The Pope last made an appearance at his hospital window on Sunday, looking frail but alert.
Reports say he has been regularly saying Mass for his doctors and nurses.
The Polish-born Pope has also long suffered from Parkinson's disease and crippling hip and knee ailments.
Amid speculation that the pontiff may resign because of illness, a Vatican official has suggested he could continue his duties even if he loses the power of speech.
"It is sufficient that one's will be expressed and be expressed in a clear way," Cardinal Mario Francesco Pompedda told La Stampa newspaper.
"It can be expressed very well through writing, and in any case can be expressed also with clear and significant gestures."