An Act MP who is leaving Parliament due to ill health said he's conceded he's "stuffed", and urged MPs to continue fighting for farmers.

Mark Cameron and former health minister Dr Shane Reti delivered their valedictory speeches at Parliament on Wednesday.

Cameron was leaving Parliament after six years, saying kidney failure, acute heart failure, and his son's death to suicide had taken their toll.

"We all have our s..., as we say in rural New Zealand, and I have certainly had my fill," he said.

Cameron recalled deciding he was going to "carry the world on his shoulders" despite his poor health.

"I remember fairly recently sitting in the chamber, house duty, nauseous, kidneys at 8% - most of you wouldn't have known this - bugger all left," he said.

"I conceded that I was stuffed."

But Parliament and farmers had given him a purpose, he said.

"I needed to carry on, so I did dialysis in my flat, and I went back to bloody work."

That was despite knowing his time as an MP would be cut short eventually, he said.

"We agreed farmers needed to be kept out of the ETS, methane limits reduced, private freshwater assets managed better and in the hands of owners, and stupid winter grazing rules fixed," Cameron said.

"At 8% kidney function, I could be a passenger in this reality, or a proponent for better outcomes and change. So here I am."

Cameron urged MPs to believe in rural people.

"They're worth fighting for, they are the economic spine of this country.

"And remember this, it is always hard to argue that fact when your mouth is full of their food."

He thanked his party leader David Seymour - a "bloody legend" - and its deputy Nicole McKee, "an awesome sister, the one I wished I'd always had".

Reti's speech followed after.

Former health minister Dr Shane Reti. Photo: RNZ

He was the MP for Whangārei - the first Māori to win the seat - and had been in Parliament since 2014.

Reti served as National's deputy leader under Judith Collins, and was health minister this term, before being demoted in January last year - replaced by Simeon Brown - when health became an increasingly problematic area for the government.

Reti detailed his highlights throughout the years, and most recently as health minister, which included the medical school at Waikato hospital, "the biggest funding increase ever in cancer drugs", and extending the breast cancer screening age group from 70 to 74.

But he had unfinished business, too, he said.

"To the fizzy drinks industry, I was coming for you, and you knew it."

Reti said he had been working on a policy to stop the industry adding more sugar to their drinks in New Zealand, versus Australia which had 40 to 50% less sugar.

"I say to the fizzy drink industry: Please explain why you have been deliberately sugaring up New Zealanders, and then reformulate to at least the baseline in Australia."

Reti said serving the people of Whangārei had been a privilege, and thanked his colleagues and family.

"Thank you all for your understanding when Papa Shane missed your birthdays, recitals, or sports events, I will do better."