Italian Prime Minister Romano Prodi has asked the Senate to back his government ahead of a crucial confidence vote, as he faces calls to resign.
Mr Prodi says he wants the vote for the sake of the nation
Mr Prodi had been advised by President Giorgio Napolitano to avoid the vote, which he looks to be at risk of losing.
The debate has been lively, with one senator carried out after fainting.
If Mr Prodi is defeated, he will be forced to step down which could trigger snap elections, which former PM Silvio
Berlusconi is well placed to win.
The crisis started with the desertion of a small party in his centre-left coalition.
Mr Prodi won a confidence vote in the lower house on Wednesday, but the loss of Udeur's three seats in the Senate leaves him, on paper at least, without a Senate majority.
Mr Napolitano was reported to have advised him to consider resigning instead of going ahead with Thursday's Senate vote.
In a 10-minute speech to senators, Mr Prodi warned that a defeat for the government would mean paralysing political action for weeks until a new coalition could be formed, or new elections held.
"Stopping the government's work is a luxury Italy cannot afford," he said.
He said the country needed continuity and backing the government would allow it to deal "urgently" with electoral reform, economic renewal and its role in international affairs.
Nuccio Cusumano (centre) fainted after reports of abuse and spitting
The BBC's Christian Fraser says it is possible that Mr Prodi was betting on a late rally of support by pushing ahead with the vote.
At one stage it seemed he had won a much-needed defection when Udeur senator Nuccio Cusumano announced he was breaking with his party to back the government, say Italian media reports.
But the response forced a brief suspension of the session after shouts that the senator was a "traitor" and a "clown" and one senator making a hand gesture as if to shoot Mr Cusumano.
Mr Cusumano was reportedly spat upon, and then fainted, before being carried out on a stretcher.
The crisis was sparked by the withdrawal on Monday of the centrist Udeur party - with its three seats - from Mr Prodi's ruling coalition, costing the prime minister his Senate advantage of two.
The party pulled out, citing a lack of support for its leader, the former Justice Minister Clemente Mastella, who resigned after being named in a corruption probe. He maintains that he is innocent.
HAVE YOUR SAY
If Berlusconi is the other alternative, then I certainly hope Prodi can survive.
Jim Bo, Sweden
The embattled 68-year-old premier won Wednesday's Chamber of Deputies vote by 326 votes to 275.
But his hopes of mustering enough support to carry the Senate and save his 20-month-old, centre-left coalition look increasingly forlorn, analysts say.
Mr Berlusconi, a conservative former prime minister who was defeated by Mr Prodi in 2006 elections, wants to see the premier defeated in the Senate.
This would trigger calls for snap elections, which polls suggest Mr Berlusconi's centre-right Forza Italia party could win comfortably, our correspondent says.