Michigan election officials are expecting between 15 percent and 20 percent of the state's registered voters to cast ballots in the presidential primary election.
Voters who choose a GOP ballot Tuesday can choose between Mitt Romney, Rick Santorum, Newt Gingrich and Ron Paul. Seven other Republicans on the ballot no longer are active or haven't mounted major campaigns.
President Barack Obama doesn't have any competition in the Democratic primary, but votes for him won't count. Democrats will choose their favorite at a May 5 caucus.
About 21 percent of the state's registered voters participated in Michigan's 2008 presidential primary, when Republicans had a contested race but Hillary Rodham Clinton was the only major Democratic candidate on the ballot.
Polls are open from 7 a.m. EST until 8 p.m. EST Tuesday.