The bitter divisions over an overhaul of the health care system have exploded at town-hall-style meetings over the last few days as members of Congress have been shouted down, hanged in effigy and taunted by crowds. In several cities, noisy demonstrations have led to fistfights, arrests and hospitalizations.

Democrats have said the protesters are being organized by conservative lobbying groups like FreedomWorks. Republicans respond that the protests are an organic response to the Obama administration’s health care restructuring proposals.

There is no dispute, however, that most of the shouting and mocking is from opponents of those plans. Many of those opponents have been encouraged to attend by conservative commentators and Web sites.

“Become a part of the mob!” said a banner posted Friday on the Web site of the talk show host Sean Hannity. “Attend an Obama Care Townhall near you!” The exhortations do not advocate violence, but some urge opponents to be disruptive.