Dr David Gillespie wants another chance to topple Lyne MP Rob Oakeshott but he must have success in the July 1 preselection vote first.

Army officer Brett Sprague is another preselection candidate.

The party expects a strong field of candidates to line up for the preselection.

Rank and file party member votes will determine The Nationals' candidate to challenge Mr Oakeshott in the federal election.

Dr Gillespie beat former Port Macquarie-Hastings councillor Jamie Harrison and Taree-based solicitor Quentin Schneider for The Nationals' Lyne preselection in 2010.

Mr Schneider will not seek preselection this time, while Mr Harrison is still considering whether to lodge a nomination.

Nominations close on Friday with the preselection vote set down on July 1.

Dr Gillespie, who went head-to-head with Mr Oakeshott at the 2010 election, is focused on the preselection process.

"I want the members to think I'm the best person to represent their ideals, business, family and values of the party in parliament," he said. "The party represents the best of Australian values and I want the members to know, in voting for me, I'm the best person to represent their values, their ethics and political beliefs."

Dr Gillespie said he hoped the party members would look on him fondly.

"It's a strong grass-roots party and there's lots of excellent candidates who will be putting their hands up," he said. "What I'm hoping to offer the party is someone who will work hard for the community, understands what the community is looking for, and has appreciation and understanding to a degree to other challenges their business and their lives have," he said.

Dr Gillespie said he hoped to do an even better job for the party this time around.

This is the 20th year the specialist gastroenterologist and physician has lived in the Hastings.

The 54-year-old is married with three children.

Meanwhile, Mr Sprague believes his army experience has equipped him well for a bid at political life.

The artillery officer in the reserve regiment would resign from the army as soon as the election was called if he won the preselection ballot.

"I'd like to think my professional history stands for itself almost," Mr Sprague said. "I'm not into getting rich ... I'm here to serve and I think serving federally is a step above serving in the military."

Mr Sprague has family in Port Macquarie, owns a house here and plans to settle here once he leaves the army.

He was a chiropractor before he joined the army and his family members have businesses.

"I understand small business but I understand intimately small business in this environment," Mr Sprague said.

The 40-year-old is also concentrating on the preselection process.

"I have to speak to a lot of people, shake a lot of hands and ask for a lot of votes," he said. "That is how I am going to win this but I still have a lot of work to do."

The Nationals preselection is one step in the battle for Lyne held by independent MP Rob Oakeshott.