Rick Santorum did not fulfill the requirements to make the ballot in Indiana, the Indiana Republican Party announced Friday.

The primary is not scheduled until May 8.

Candidates needed 500 verified signatures from each of the nine congressional districts in the state.

The Indiana GOP told ABC News that Santorum fell short in the seventh congressional district, where the state capitol and largest city, Indianapolis, is located.

The state does not allow write-in candidates, but Santorum told reporters Friday in Fulton, Mo., that the campaign is challenging the decision.

"We just found 29 signatures we believe will be ruled valid in Indiana. Should put us on the ballot," Santorum campaign officials said.

He blamed falling short of the signature requirement on redistricting and signatures that were disqualified. The former Pennsylvania senator said he's confident he will end up on the ballot.

"From our perspective - and they invalidated a whole bunch of signatures - we're going to review," Santorum said. "We're only 24 short. They invalidated 200 that they said were not good because of ditto marks, things like that. We're going to go back and look. We have to make up 24 signatures and I think the fundamental issue is you can't have petitions circulated and have one district be one thing and then half way through have the district change and not count the signatures that were given at the time that they were in fact in that district. So we've got some very credible, I'm sure solid, legal challenges, and I have no doubt that we'll be on the ballot there."

Mitt Romney, Newt Gingrich and Ron Paul all made it on to the Indiana ballot.

Santorum has consistently said that he will continue to stay in the race for the long haul and collect delegates up until the convention, but this marks the second state where he won't be on the ballot and, therefore, not eligible to collect delegates.

He also did not qualify for the ballot in Virginia where there are 49 delegates at stake (Only Mitt Romney and Ron Paul qualified). In Indiana there are 46 delegates at stake.

Both Virginia and Indiana are states where delegates are allocated proportionally, as opposed to "winner takes all," meaning these are states Santorum could ride out of with delegates despite not claiming victory.

Just last month in South Carolina, Santorum told reporters how important it was to get on the ballot in every state, pointing out that despite having a "campaign that was surviving on oxygen through a swizzle stick" they made getting on ballots a priority.

"We actually made decision in December while we were sitting at 2 and 3 percent in the polls, in the national polls, not to put money in Iowa and actually to put money to getting on state ballots - in December when people were saying you need to get on TV, if you don't do well in Iowa you aren't even going to get on these states, and we always believed in that, so I think you have to look at, given the resources we had, it's amazing the states that we are on," Santorum said. "And I think it shows a hopefulness and an optimism that our campaign always believed when every reporter was asking us, 'Why are you in this race?' We were putting $5- and $10,000, which was a ton of money for us back in December, [into] Oklahoma, Louisiana and places like that, so it's really paid off for us."