* Tuesday, polls open 7 a.m. to 8 p.m.
WHO CAN VOTE:
* Registered Democratic and Republican voters. The state's independent ("declined affiliate") voters can only vote in non-partisan local races, such as school board or, in Carroll County, charter board members.
WHO'S ON THE BALLOT:
* Candidates for President, one U.S. Senate seat, all eight House seats, delegates to the Democratic and Republican conventions and local judges.
* Six Democratic presidential candidates: Edmund G. Brown, Jr., Bill Clinton, Tom Harkin, Bob Kerrey, Lyndon H. LaRouche and Paul Tsongas. Two Republican candidates: Patrick J. Buchanan and George Bush.
* Three other candidates were unable to get on the Democratic ballot: Baltimore socialist Robert Kaufman, former Minnesota Sen. Eugene McCarthy and former Irvine, Calif. Mayor Larry Agran.
* There are no provisions for write-in candidates in the primary.
* Voters also can choose "Uncommitted to any presidential candidate," on the Democratic ballot. Republicans have no uncommitted slot.
* Democrats and Republicans will also select delegates who are pledged to presidential candidates at the party convention this summer. Democrats can also select uncommitted delegates.
* Democratic delegates will be apportioned based on the percentage of the vote their candidates win in a congressional district. On the GOP side, the victor in a congressional district collects all the delegates.
* Democrats will choose 44 delegates and 8 alternates, allocated to each of the eight congressional districts based on redistricting from the 1990 census and on the district's history of supporting Democratic candidates.
* Republicans have 24 convention delegates, with each of the eight congressional districts receiving three delegates. The winning delegates will select their alternates.
* Democrats and Republicans will be choosing candidates for a U.S. Senate seat. Incumbent Democrat Barbara A. Mikulski is vying for a second six-year term, facing six other Democrats. Fifteen Republicans are running for a chance to battle the Democratic candidate in the fall.
* All The state's eight congressional seats also are up for grabs. And the primary will be the first chance for voters to cast ballots in districts redrawn last fall during the once-a-decade congressional redistricting.
* The new districts include a majority-black 4th District in the Washington suburbs, forged to comply with the federal Voting Rights Act.
* In the 1st District, newly configured to extend from Curtis Bay in Baltimore to Crisfield on the lowest reaches of the Eastern Shore, two incumbent congressmen have been thrown in together: Representatives Tom McMillen, D-Md.-4th, and Wayne T. Gilchrest, R-Md.-1st. Both lawmakers face primary challengers.