Health minister Tony Ryall is to quit politics at the election, taking to 14 the number of National MPs who have left or signalled they are leaving.
Ranked No 6 in the Cabinet, Mr Ryall is the highest-profile retirement yet.
Prime Minister John Key said there were always different reasons why people left politics. "People don't come into Parliament and stay there generally for 40 years . . . It's just one of those things."
And he said National had far more talent than Labour, which has had only one retirement announced so far ahead of the election.
"There's little on their front bench. David Parker . . . wouldn't be a quarter of the performer Bill English is, and you can go all the way down the line."
Labour leader David Cunliffe's response was to label Mr Ryall the latest in a string of "Nats off a sinking ship".
"They're like lemmings over the edge of a cliff," he said.
Mr Ryall will stay on in his portfolios, which include state-owned enterprises, until he bows out at the election. He had no specific job in mind after politics, although he was interested in a private sector role.
Mr Key praised his long service to New Zealand during his 24 years as an MP - he came into Parliament in 1990, aged 26 - and said he had been "an extremely effective" minister.
"Tony will leave the health service in far better shape than he found it back in 2008 and, while we are really sad to lose him, we support his decision."
Conservation Minister Nick Smith, Mr Ryall's close friend, said he was disappointed from a government point of view but totally understood his departure from a personal standpoint.
They had private discussions about it for some months and Mr Ryall - who would remain a lifelong friend - had told him about his decision at the weekend.
"Tony is a very good mate. He and I and Bill English entered Parliament together in 1990, we were branded the brat pack by Sir Robert Muldoon, and the label has unfortunately stuck."
Dr Smith said he would not leave and was absolutely committed to another term.
National Party president Peter Goodfellow said Mr Ryall had made an "outstanding contribution".
"I believe anyone who has worked closely with him would agree with me when I say he is one of the best health ministers this country has seen."
But Opposition MPs were not sorry to see Mr Ryall go.
Labour state-owned enterprises spokesman Clayton Cosgrove questioned the timing of the announcement, coming after the Government announced a possible wind-back in the size of the next partial asset sale.
"The day after they wave the white the flag on Genesis Energy, Mr Ryall takes a dive," he said.
Green Party health spokesman Kevin Hague said his departure would leave questions unanswered over a potential fraud case involving public money.
"His decision to resign does not absolve him from his responsibility to explain his part in the disagreement between South Link Health and Southern DHB," Mr Hague said.
The Southern District Health Board has been in a battle since 2003 with Independent Practitioner Association-controlled South Link Health over the funds, which could amount to as much as $15 million.
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