Mike Groll/Associated Press

Bill Owens became the second of two new Democratic congressmen in the House of Representatives early Friday afternoon, as he was officially sworn in after a raucous special election in New York’s 23rd district.

Both Mr. Owens and California’s former Lt. Gov. John Garamendi, who was sworn in on Thursday, lend two critical votes for the Democrats’ much-desired 218 tally required to pass the health care bill this weekend.

Harry Hamburg/Associated Press

Mr. Owens defeated Douglas Hoffman, a candidate on the Conservative Party line in upstate New York, after conservatives rallied around him against the Republican, Dede Scozzafava, who dropped out. He replaces John McHugh, a Republican, who was selected by President Obama to become secretary of the Army.

Mr. Garamendi replaced Ellen Tauscher, the California congresswoman who became an undersecretary in the State Department.

The House membership is now at 435 representatives.