The fiercest congressional contest is in the 6th District, where Republican Richard Tisei is challenging Rep. John Tierney.
Tisei has accused the seven-term Democratic incumbent of being dishonest with voters about what he knew of an illegal offshore gambling ring run by two brothers-in-law.
Tierney has faulted Tisei for using what he called smear tactics and said he’s sold out to tea party extremists.
If he wins, Tisei, who is gay, would be the first Massachusetts Republican elected to the House since 1994.
Voters will also be choosing state senators and state representatives, although Democrats’ firm hold on power in the Massachusetts Legislature seems unlikely to be loosened, with Republican candidates running in less than half of the legislative seats.
Polls are open Tuesday from 7 a.m. to 8 p.m.
Salsberg reported from Lowell.