A group backing gubernatorial candidate James Blanchard has raised more than $660,000 and spent most of it on ads promoting the former governor.
Citizens for Responsible Leadership paid more than $300,000 to a Washington media company to prepare a series of television ads.
It also spent more than $340,000 to air the ads this month on network and cable stations in Detroit, Flint, Lansing and Marquette.
Thursday was the deadline for independent political action committees to file their second report of the year.
Candidates and political parties must file campaign finance reports by Friday.
Blanchard is running against Congressman David Bonior and Attorney General Jennifer Granholm for the Democratic gubernatorial nomination.
The St. Clair County Democratic Committee has run several TV ads on Bonior's behalf.
Granholm has been helped by campaign mailings sent by the Michigan Education Association and a national pro-choice group.