If the experiment is successful, it could be a major boost to the Internet-voting movement.
"We realize that the eyes of the nation are upon us, so we want to make sure the process is bulletproof," said Cortland Coleman, interim executive director of the Arizona Democratic Party.
Arizona, a state with 843,000 registered Democrats, generally sees low turnout during the presidential primaries. But advocates and party leaders believe the Web will shake voters into action this year.
In the 1996 primaries, about 13,000 Democrats voted. This year, the party is counting on that figure to jump to around 50,000.
The experiment has not gone without controversy.
At first, justice officials worried that the push for online voting would disenfranchise poor and minority groups that frequently don't have access to computers.
Equally troublesome were security issues. Officials didn't want hackers affecting the election outcome.
But party officials have quelled those fears for now.
Coleman said there will be 29 more polling booths in low-income neighborhoods than in the 1996 election. And to offset security concerns, officials have hired a team of experts to fend off any attacks.
The online voting project was made possible through a company called Election.com, which also is launching software that will allow voters to register on the Web.