Black smoke rising from a chimney above the Sistine Chapel indicated that their ballot had been unsuccessful.
The 115 cardinal-electors will vote four times daily until two-thirds can agree on a single candidate.
The election was prompted by the surprise abdication of Benedict XVI. There is no clear frontrunner to take over from him as head of the Church.
The cardinal-electors earlier attended a special Mass in St. Peter’s Basilica.
At this morning’s “Mass for the Election of the Supreme Pontiff” they sought divine guidance for the election ahead.
In his homily, the Dean of the College of Cardinals, Cardinal Angelo Sodano praised the “brilliant pontificate” of Pope Benedict and implored God to grant another “Good Shepherd” to lead the church.
Earlier this afternoon they retired to the Sistine Chapel to begin their secret deliberations.
The 85-year-old Benedict XVI stepped down last month saying he was no longer strong enough to lead the church, which is beset by problems ranging from a worldwide scandal over sexual abuse to allegations of corruption at the Vatican bank. (BBC)