The results brought the Democratic numerical roster to 90 in the 151-seat House, leaving Republicans with 59. There are two House independents.
"It's been more than 10 years since a single political party held 90 seats in the Maine House of Representatives," said House Speaker Glenn Cummings, D-Portland. "We're very proud of all of our candidates."
Maine Republican Party Executive Director Julie O'Brien said the outcome should serve as "a wake-up call" for Republicans.
According to unofficial returns, Democrat Mike Carey defeated Republican David Hughes in District 72, which includes part of Democratic-leaning Lewiston.
In District 83, which includes Belgrade and Vienna, Democrat Patricia Jones of Mount Vernon beat Republican Clyde Dyar, also of Mount Vernon. Democrat Sheryl Briggs of Mexico beat Republican Katherine Harvey of Dixfield in District 93, which includes Canton, Carthage and Peru, unofficial returns show.
Briggs' victory in the district previously represented by Republican Randy Hotham gave Democrats their pickup.
Jones will succeed her late husband.
Maintaining a GOP hold on two seats, Republican Ralph Sarty Jr. beat Democrat Kate Smith in District 99, which includes Baldwin, Cornish and Sebago, and Republican Peter Johnson of Greenville won a three-way race in District 27, which includes the towns of Brownville and Monson.
The five special elections resulted from three resignations and two deaths. Three of the seats had been held by Republicans, two by Democrats.
"We're all excited for Mike, Pat and Sheryl to join our caucus. ... They will all make fantastic legislators, and I'm looking forward to getting down to work with all of them in January," House Majority Leader Hannah Pingree, D-North Haven, said in a statement.
O'Brien said the Republican loss in District 93 occurred in an area favorable for Democrats and where Hotham's success as a GOP candidate had been "kind of an anomaly."
More generally, she said, "Democrats do very, very well at mobilizing volunteers, getting out the vote ... To be honest, Republicans need to take a lesson from that."
A year ago, statewide voters put 88 Democrats and 61 Republicans in the House, along with two independents.
Lawmakers are scheduled to reconvene in January for the 2008 regular legislative session.
Statewide, a legislative initiative to ease restrictions on consecutive service in office by members of the House and Senate was overwhelmingly rejected by voters.

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