Still not committed either way is Rep. Bart Stupak, D-Mich., the leader of a Democratic faction that wants stronger anti-abortion language in the legislation.
Some Democrats seemed to believe they could pass the bill without further changes to appease Stupak.
"We've compromised enough," said Rep. Diana DeGette, D-Colo. "The bill's not going down."
But Republicans also are wooing undecided Democrats. And though they don't have the votes to defeat the measure on their own, they are trying to make as much noise as possible.
They got some help today as thousands of the Republican faithful and other health care reform opponents filled the steps of the U.S. Capitol.
However, in some cases, the opposition got ugly.
Democrats claimed a protester spat on Rep. Emanuel Cleaver II, D-Mo., and referred to Rep. John Lewis, D-Ga., with a racial epithet. A spokesman for Cleaver said a suspect was arrested but the congressman declined to press charges.
In addition, officials said anti-gay epithets were hurled at Rep. Barney Frank, D-Mass.
Republicans focused their lobbying efforts on approximately 15 Democrats viewed as swayable.
Rep. Charles Boustany, R-La., who is a doctor, was working on some of the freshman Democrats.
"It's very fluid right now and we're going to continue to work," he said, adding that Republicans were doing "anything we can do to bring the pressure to bear to get them to think about what the implications are for a yes vote."
The only Republican who voted for an earlier House version of health care reform reluctantly flipped.
"Tomorrow will be a sad day for me as I cast a no vote against something I believe we need, to prevent the expansion of abortion," said Rep. Anh Cao, R-La.
One Republican has accused the administration of offering jobs to Democrats who flip to yes votes and then lose in the November elections. A Republican senator issued a warning to Democrats, saying if that scenario plays out, he will block any nomination that comes before the Senate.
ABC News' Z. Byron Wolf and Vija Udenans contributed to this report.