Of 33 Senate seats up for election this year, Indiana's is among only five called toss-ups at this point by independent polling firm Rasmussen Reports.
The others are in Massachusetts, Montana, New Mexico and Virginia.
Rasmussen said the Indiana race between Democrat Joe Donnelly and Republican Richard Mourdock "remains a dead heat" according to a poll it commissioned last week.
State Treasurer Mourdock was favored by 42 percent of likely voters, while Donnelly, who represents Indiana's 2nd District in the House, was supported by 40 percent. The margin of error was 5 percentage points.
The Indiana poll was conducted July 31-Aug. 1 of 400 likely voters. Forty-five percent were Republicans, 32 percent were Democrats, and 24 percent were identified as "other."
A Rasmussen survey in late May among 600 likely Hoosier voters had Donnelly and Mourdock in a tie, with each preferred by 42 percent of those polled.
Here are some of the findings of the latest poll:
Mourdock gets the edge among women, 43 percent to 39 percent for Donnelly.
Mourdock enjoyed a 14 percentage point lead among voters older than 65, while Donnelly held a 14-point margin among voters younger than 40. More than half of the respondents were between those ages, and Mourdock had a 10-point lead among them.
Among income groups, Donnelly's highest rating was 57 percent among people who earn less than $20,000 a year, while Mourdock's best showing was 55 percent among those earning $60,000 to $75,000. But 46 percent of those earning more than $75,000 were undecided.
Donnelly was favored by 81 percent of likely black voters and Mourdock by just 2 percent, while 17 percent of blacks said they would prefer "some other candidate." Only 6 percent of respondents were identified as black.
Rasmussen found that of the 43 percent of Hoosiers who strongly favor the repeal of the federal health care law, 81 percent would support Mourdock. And of the 26 percent of respondents who strongly oppose such a repeal, 95 percent would back Donnelly.